cadiman1949

I really appreciate you starting this thread... I will be going by my dealer today to see if they have made any progress with a diagnosis of my engine noise. If they have not I am going to start the process of going up the food chain starting with the service manager and they the regional service manager. After doing my homework I have found this issue discussed in several places over the last year of so on several different forums. Seems to be an issue with any engine that has that V-4 mode and AFM. I firmly believe that GM is hiding from this problem.

I just purchased the car a few weeks ago and I knew there must be a problem or the man selling would not have gotten rid of such a nice car so soon after buying it. I was just surprised to see how long the problem had been going on and how poorly the dealer addressed the issue. I think the man sold the car because he believed the dealership was not capable of fixing the problem and he was not filling to fight the manufacture through our State's "Lemon Law". Here is a timeline on what happened with my Z06 according to the dealer service records. The car has had several oil changes and I'm not going to list them in this time line...

03/15 Car placed into service with original owner 3 miles
07/15 Customer complains of rattle noise from exhaust 2954 miles
(Dealer claimed noise was from flywheel and ordered parts)
08/15 SOP order flywheel installed 3776 miles
(at dealership 4 business days)
01/16 SOP Belt tensioner installed 4895 miles
(another complaint of a rattling noise)
02/16 Noise from engine and wont idle on it's own 7786 miles
(spun crankshaft main bearing replaced complete engine)
(at dealership for 16 business days)
05/16 Customer complains vehicle has Transmission Rattle 9837 miles
(dealership lubed exhaust pipe control valve)
(dealership could not duplicate noise & needs customer to drive more)
(at dealership for 2 business days for engine noise)
06/14 (Install SOP exhaust actuator)
(yet another attempt to fix a rattling noise coming from engine)

10/16 After only owning this car a few days I was hearing all kinds of noises and odd vibrations coming from the engine and possibly the transmission. I made 2 visits to the same dealership that did all the work on this car prior to dropping the car off on October 24th. I spoke with the Corvette technician at this dealership and explained to him that I was able to duplicate the "rattling" noise any time I wanted and that it was without doubt coming from the engine and there may be another coming from the transmission. I left 1 full page typed notes of when exactly the noises and vibrations happened with the Corvette technician at this dealership a few days prior to me leaving the car so he might have time to study the complaint. I am a technician of more than 32 years so I know how to talk to another mechanic. I took the Corvette technician at the dealership for a ride prior to leaving the car on the 24th (the same day I left him my typed page of notes) and the service writer on the 24th and was able to easily duplicate the noise many times is a short ride for both of them.

As you all can see the complaint of "rattling noises" started just a little under 3000 miles on my car and being only 4 months old. The noise always seems to start by being very slight and hard to duplicate and progressively gets worse with time and miles. It does not just effect only 2014 to 2016 Corvettes. The problem appears to be related to any vehicle equipped with the LT family V8 engines and automatic transmission with V4 capability and AFM systems. It's a problem that occurs while cruising at a steady speed driving with low engine RPM and then applying at light throttle, while in V4 mode, to slightly increase your speed... (always when shifting from V4 mode to V8 mode). In other words normal city driving.

I hope to have some more news today... I'll keep you all posted on what actions are being taken.

cadiman1949

Went by the dealership today to see how things are going on the repairs of my Z06. Turns out the mechanic and the service writer are both off today...

dckotwicki

Thanks for your response.
Please keep all of us posted.
Good luck.

BOBSZ06

Replaced the belt tensioner today to see if that would eliminate or reduce the "flutter" or "rattle" I have notice intermittently.

The "Rattle" is still there intermittently while in V4 mode. Does not do it all the time and mostly at higher speeds.


Apparently it is the Lifter Oil Manifold Assembly (LOMA) as shown above in the #40 and mentioned in #44 post.

cadiman1949

I sent an email on Monday to my Service Adviser and got no response. Stopped by dealership Monday afternoon and found the Mechanic and Service writer were off on Monday. Got a reply to my email on Tuesday morning from the service writer saying he would talk to the mechanic and get back to me. It's now Thursday morning (November 3rd) and I have heard nothing. My Z06 was taken to the dealership on October 24th. They are not telling me it's normal and they are not telling me they can fix it. Might be time to make an appointment with the service manager and/or regional service manager. I'll wait until this coming Monday for someone at the dealership to give me some information and if the Service Adviser doesn't talk to me by it might be time to speak with the service manager and find out what is going on and what can be done...

Anyone else information and/or advise on how best to proceed?

cadiman1949

This is the best way I have found to make your C7 with an automatic transmission make the "Rattling Noise" or "Rumble Strip" noise being talked about I this post while in V4 mode and when shifting out of V4 into V8 mode. I know this works with the LT4 in my Z06 but I bet it works with any 2014-16 C7 regardless of engine as long as you are equipped the A8 automatic transmission.

First get the car warmed up by driving it for 10 minutes or so (normal city diving)

Find a road near you that is fairly smooth and flat that has longer stretches that you can drive the car 25 to 40 mph without hard curves, few stop lights or stop signs so you can maintain speeds for 10 to 30 seconds at a time.

While on that road set your cruise control at 25, 30, 35 or 40 mph (based on the speed limit of your road).

Make sure you are in V4 mode first... then by using the cruise control switch lower your speed by 1 mph. You will note the noise will become less or may even go completely away. Once the speed normalizes increase your speed by 1 mph... (again you need to be sure you are in V4 mode).

At the point you command the cruise to increase your speed by 1 mph you will hear a very pronounced "rattling noise" (if your car has the same problem as many of the cars in this post).

Be patient and drive easy and if you have an AFM problem you will hear the noise that was recorded in the earlier pages of this post.

Hope this help a few of you duplicate the problem...

cadiman1949

The person who started this post was very happy that the discussion went as far as it did. I believe that person lives in cold-country and is putting the Corvette away for the winter. I remember that the original poster asked that we keep this post going so they might be able to learn more about their own Corvette. I am very thankful for what you posted because it has given me lots of ammunition to fight GM with the problems I am having with my car.

I am very happy that you are getting your car back! My car too had the exhaust control in the exhaust system was lubricated on my car as well.

My car has now been at the dealership for two full weeks. I spoke with the mechanic yesterday and he did an update on a transmission issue where it was slow to go into gear and he told me he did tests on the transmission torque converter that were clearly out of the specs that a GM service rep gave him. He followed the procedure to the letter which was given to him by GM directly and GM will not give him any answers on how to proceed with that issue...

Then the mechanic informed me he told the GM rep that the noise in my engine is there, it's real and that he does not feel it is normal. In fact the noise is now worse from what he recalls it sounding like earlier this year. The mechanic informed the GM rep that the car has a new owner and that I (the new owner) brought the car back in to the dealership with the same complaints that the original owner had. The mechanic explained that I was much more able to explain and clarify what I was noticing and the I knew how to describe it with great detail. The GM rep told the mechanic that he must do more testing and then in the same breath told the mechanic GM will not authorize any time to pay the mechanic for his time to do these tests. Dealership mechanics only get paid for work they actually perform and only get paid for diagnosis if it is pre-approved. Also... the dealership service manager is not giving the mechanic this authorization because GM will not approve it under warranty and does not want the cost coming out of his profits... I can't say I really fault the mechanic for not being excited about working for free but the service manager is being a ***** about this as well. I believe the dealership thinks this is going to make me give up and go away... they are sadly mistaken and I let the mechanic know that. I will not be pushed around and the dealership along with regional GM rep are going to be hearing from me very soon. I'll let them goof-off for one more week and then I'm going to get serious about GM taking this car back. If they are unable or unwilling to fix it they will leave me with no choice but to proceed with "lemon Law" actions!

Anybody think I wrong?

BOBSZ06

Second drive with new belt tensioner........

Definitely a change in the characteristics of the "noise".

1. The noise has gone from a "more muted flutter" to a "rattle" when it occurs;
2. Speed: Only now notice the noise when 60+ mph; before at a variety of speeds.

At 60+ mph and when switching from V8>V4 mode I intermittently notice the "rattle"...not always. Just the right load and it will occur.

BOTTOM LINE: It IS the Belt Tensioner causing the noise.
A result of the load change when V8>V4 and the belt tightness on the belt tensioner causing the tensioner to vibrate.

Note: The belt tensioner in the LT1 (stingray and GS) is of a different design than the LT4 (Z06). Not many reporting this issue with the LT1 engines.

INHERENT IN DESIGN! It is just a problem associated with the belt tensioner design on the Z06 and one most will notice.

Use the Manual mode instead of Auto mode of driving or get the Range device to eliminate the V8>V4 switching which causes the load change on the belt tensioner.

CASE CLOSE.

cadiman1949

Bob, is your car a Z06 or a Z07? I ask because the Z06 engines were built on Tonawanda NY and the Z07 engines were built at the special engine plant at Bowling Green... Seems that the Z07 engines are less problematic as they were all hand assembled as the Z06 engines were built on Tonawanda line along with truck engines. Just would like to know so I can continue to compile the information.

Hello Bob,

Did you try driving your car the way I described in one of my earlier replies? I can make my car "rattle" or sound like it is driving over "Rumble Strips" at any speed between 15 and 65 mph at will. I posted a starting speed 25 mph because that is the lowest speed the cruise control will activate to make the noise easier to duplicate.

My Z06 and it has gotten a new belt tensioner twice and the noise has not changed to speak of. The noise in my engine is not intermittent and will "rattle" every time I drive it. The VOLM part of the AFM system appears to be the problem area as it affects some high end Chevy, GMC and Cadillac trucks (as well as Corvette) with engines built at Tonawanda and there are service bulletins on the LT-1 LT-4 and some 5.3L & 6.2L truck engines about the VLOM. If I am not mistaken some of the "V" series Cadillac cars are having a similar issue you are describing with the belt tensioners that relates to what you are talking about.

As for my Z06 the noise is without a doubt coming from the engine and it is a metal-to-metal sound. It is a solid noise that is not mistakable and does not sound like the belt tensioner noise that some have recorded. The first recordings of the "Rumble Strip" noise earlier in this post are very different that the noises recorded for belt tensioner problems. I have to say the case is not closed and the "Rumble Strip" noise is completely unrelated to the belt tensioner.

Please let us know if you try driving like I described and if you have a Z06 or Z07.

Kindest regards,
Rick

BOBSZ06

I have a `15 Z06 same engine/belt tensioner as in the Z06 w/Z07 option.
The new belt tensioner that I installed made a definite change in the "noise" characteristics that I notice.

-Used to notice it at multiple speeds....now only over 60+
-Made a flutter sound before; now rattle.

No question the change in the tensioner has made a difference.
Note: the difference seen in the noise is likely due to the new stiffer tensioner spring that keeps the metal stop on the tensioner head tighter to the stop on the tensioner body. As a result of the vibration the stops make contact and thus the "metal" noise or rattle. This vs. the more worn tensioner that isn't as tight and does not make this contact with only the vibration of the tensioner head with the belt, and at many different speeds since the spring is not as tight.

Again, it is inherent in the design of the belt tensioner on the Z06 engine and new belt tensioners will not solve the problem only possibly make it sound different and at different conditions.

Certainly, there could be an issue with ones LOMA but for most it is the belt tensioner design.

Belt Tensioner...Why?
I pointed out in a prior post that there is a technical service bulletin out regarding the belt tensioner in the LT1, Stingray that when it leaks and as a result does not tension as properly as it should, a noise, flutter or rattle is noticed:

https://www.corvetteforum.com/forums...post1593133675

Same issue with the LT4, Z06 but in our case its the spring inside the tensioner that is the issue. With time it becomes more noticeable as the spring tension decreases due to wear and the noise, flutter or rattle, ensues.

Prevention:
1. Either manual;
2. Range device or tune to prevent the loads and belt movement due to the V8>V4 conditions.

cadiman1949

The noise that I believe is being discussed in the post is not a faint noise that can only be heard during the switch from V4 to V8 mode. It is a noise that can be heard while in continuous V4 operation that gets much louder as you slightly increase the load on the engine and instantly goes away with a loud burst of noise when the engine goes back into V8 operation.

The first time I noticed the noise I was driving my car near 40 mph with the top down on a smooth flat road with the radio on while talking to my wife. The noise came over the top of all that background noise and made us both say at the same time :What was that!". It's not a small I think I heard something kind of noise it is a what the heck was that kind of noise... The noise sounds like it is right on the other side of the firewall not the front of the engine. The noise always happens under light-steady to light throttle increase so load on the drive belt is not increased significantly...

You may have not experienced what a lot of us are hearing but the lady with the Solver Z51 started hearing the noises that were recorded on page one of this post starting around 3000 miles and then it graduated to what she recorded and posted just a few months later. My noises are not as loud as what was recorded by the lady with the Silver Z51 but it is a solid metal-to-metal sound without a doubt. Belt tensioners don't make a sound like you are driving over rumble strips on the road.

The case may be closed for your car but it is far from closed on many others of use...

I have laid out detailed instructions on how to drive your car on Page 3 of this post to duplicate the noise I am experiencing. I invite anyone else to follow those instructions and hear for themselves if their Corvette does or does not make the noise...

cadiman1949

Rather than asking people to go back to try and find my reply with instruction on how best to duplicate the "Rumble Strip" noise I and going to repost it here. The noise I am talking about sounds like it is just on the other side of the firewall. If you are hearing a "Flapping" type noise that is further away from the firewall you may just be hearing the belt tensioner. Hope this help some of you...

This is the best way I have found to make your C7 with an automatic transmission make the "Rattling Noise" or "Rumble Strip" noise being talked about I this post while in V4 mode and when shifting out of V4 into V8 mode. I know this works with the LT4 in my Z06 but I bet it works with any 2014-16 C7 regardless of engine as long as you are equipped the A8 automatic transmission.

First get the car warmed up by driving it for 10 minutes or so (normal city diving)

Find a road near you that is fairly smooth and flat that has longer stretches that you can drive the car 25 to 40 mph without hard curves, few stop lights or stop signs so you can maintain speeds for 10 to 30 seconds at a time.

While on that road set your cruise control at 25, 30, 35 or 40 mph (based on the speed limit of your road).

Make sure you are in V4 mode first... then by using the cruise control switch lower your speed by 1 mph. You will note the noise will become less or may even go completely away. Once the speed normalizes increase your speed by 1 mph... (again you need to be sure you are in V4 mode).

At the point you command the cruise to increase your speed by 1 mph you will hear a very pronounced "rattling noise" (if your car has the same problem as many of the cars in this post).

Be patient and drive easy and if you have an AFM problem you will hear the noise that was recorded in the earlier pages of this post.

Hope this help a few of you duplicate the problem...

BOBSZ06

Just got back from an hours worth of driving with my new belt tensioner.
Same as my prior post....30 - 65 mph and the only time I noticed the loud rattle from the engine area was at 58-64 mph.
All mph below 58.......Nothing!

Big change over the video shown in this Thread and the flutter noise. Same issue I was having and is now gone at speeds less than 58+ mph. Not totally gone as it does occur at higher speeds and definitely INHERENT IN DESIGN. But for now, better.

When the noise occurs it is very noticeable and not faint and no doubt was an issue with my belt tensioner.


....to be continued!

BOBSZ06

....continued........



SOURCE OF NOISE: Belt Tensioner
CAUSE OF NOISE: Belt Tensioner vibration
NOISE : Metal stop hitting against metal stop in most cases is what is heard. When the engine does its DOD, V8>V4 this causes a slight slackness in the drive belt (red line) that allows the belt tensioner to vibrate and thus hitting against its metal stop causing the noise.

Here is a pic of the two belt system used on the LT4 engine with the red line representing the drive belt to which the belt tensioner is connected.





When replacing the belt tensioner you must disengage the tensioner by using a 15mm end wrench and pushing counter-clockwise down as far as possible to get the belt loose. Getting it back on is difficult!

What is Occurring? When re-engaged the belt tensioner is very close to the metal end stop. Movement in the tensioner during V8>V4 results in these metal stops hitting each other causing the "noise".

I do not see a way to tighten this drive belt? If there was then the tensioner could be disengage slightly and the belt tightened keeping the stops further apart so they would not hit.

If anyone knows if there is a way to tighten this drive belt speak up.
Possibly with use the belt develops some looseness and this worsens the situation.

Otherwise, this is an INHERENT IN DESIGN issue that the best one can do is to change the belt tensioner so it does not vibrate as much. In my case this has helped with the noise now only occurring intermittently during high speed V8>V4 occurrences. Prior to the change the noise occurred at a variety of speeds.


Tech Forum response: https://www.corvetteforum.com/forums...djustment.html

cadiman1949

Thanks for the detailed Diagram Bob and I do not disagree that the Blower Drive Belt tensioner could cause a loud noise based on what you are showing. It's wonderful that your solution is that simple!

I still contend that if your car makes the same noise (in volume and intensity) at 15 mph as it does at 65 mph and it only happens at light throttle with light load on the engine in V-4 mode it is not the belt tensioner causing the problem. The engine load required to maintain 25 mph is significantly less than what it take to maintain 60 or 65 mph. The noise that I, and many other, are experiencing does not show itself If you are asking for moderate to high power from the engine. It is RPM more specifically sensitive to low engine speeds and only happens when the VLOM is active during AFM operation.

I have heard belt tensioner noises and I have heard internal engine noises in my 32 years as a professional master auto technician and shop owner and the noise I am hearing is NOT belt tensioner but internal engine noise. If it were a belt tensioner making noise on my car I would have it back 2 weeks ago...

I am very happy for Bob and anyone else who can have their issue either changed or completely corrected with a new tensioner. The fact remains that there are still more than a few of us who have deeper issues with their cars that can be potentially much more expensive to correct should we let the manufacture feed us a line of BS to make us go away until the warranty is over and then all of a sudden have a fix that they can charge us for.

I will keep you all posted on how things proceed with my Z06. I would love to hear more from the lady with the silver Z51 on how things progress with her engine repair.

Has anyone else driven their car as I described earlier in this thread? I would love to hear from anyone who has driven their car as I described and let us know if you do or do not hear the "Rumble Strip" noise...

The case for me is far from closed for me but I still have hope that it will be resolved.

BOBSZ06

BELT TENSIONER NOISE PHENOMENON

1. This phenomenon only occurs during switching from V8>V4 under light load. The switching will not occur under load and the noise created only occurs in V4.

2. The speed that the V8>V4 occurs does not matter provided the load is light, which is when the rpms on the engine are also low and usually in the teens. The V8>V4 will not occur during load conditions on the engine.

My old Belt Tensioner would cause this noise to occur during the V8>V4 light load at multiple speeds around town and on the highway. It sounded like a pump on the rear of the drivers side and had me confounded. I initially thought...fuel pump running!

Then I found the issue with the leaking Stingray belt tensioner that was producing the "flutter" (like a pump running and my old noise) and the louder "rattle" (like metal on metal and my new noise).
It became obvious that the source of the noise in the Z06 that most are experiencing was also the belt tensioner as it would occur under the same condition as with the Stingray...light load at multiple speeds.

My new belt tensioner has changed the characteristics of this noise dramatically from the "flutter" at multiple speeds under light load > "rattle" at only high speeds under light load, ie V4.

Q. What I do not understand is why mine now only occurs at higher speed, low rpms under light load, ie V4? Should be the same at lower speeds with the same rpms. But I have not been able to get the tensioner to vibrate a the lower speeds, but same rpms.

REMEDY - This problem is an INHERENT DESIGN ISSUE but these measures can be used to reduce/eliminate the problem:

1. Change the belt tensioner. This may change the characteristics of the noise sufficiently to cause it to be much less annoying;
2. Operate in Manual drive mode. This eliminates the V8>V4 switching that causes the belt tensioner to vibrate;
3. Install a Range Disabler. This will be inserted in the OBDII port and stop the V8>V4 switching.

cadiman1949

2 belt tensioners later and the car still has noise while driving in V4 mode (continuous)... Noise is not just when switching between V4 and V8, it's there the entire time the car is in V-4 mode. The only variation is how loud it is based on the slight changes to load changes on the engine while maintaining V-4 operation... GM does not think it is a belt tensioner again...

BOBSZ06

REMEDY - This problem is an INHERENT DESIGN ISSUE but these measures can be used to reduce/eliminate the problem:

1. Change the belt tensioner. This may change the characteristics of the noise sufficiently to cause it to be much less annoying;
Being an Inherent design issue this measure will not eliminate the noise.

DONE...changed the noise characteristics dramatically.

NOTE: I would also change the drive belt for this set that includes the blower and belt tensioner. It may get stretched just enough to allow this tensioner vibration. Maybe those that drive their cars "hard" it may be the smoking gun that causes the issue.

http://www.trunkmonkeyparts.com/chev...ercharger-belt



2. Operate in Manual drive mode. This eliminates the V8>V4 switching that causes the belt tensioner to vibrate;

Normally operate my Z06 in manual drive mode 95% of the time....love the paddles!


3. Install a Range Disabler. This will be inserted in the OBDII port and stop the V8>V4 switching.

I have ordered and will install with an OBDII extension switchable connector the Range Disabler. This will eliminate any annoyance with the noise that might occur during V8>V4 switching!

With the three above measures being taken I have done all I can do at this time to reduce/eliminate the belt tensioner noise.

CASE CLOSED

BOBSZ06

Dealer needs to change out the LOMA units as it seems a likely source of the DOD (V8>V4) noise you are experiencing if not the belt tensioner or belt.

Lets us know what is found that corrects your noise problem if not a buy-out due to lemon law reasons.

dckotwicki

This noise began before I had the airbags reprogrammed.