Kenafin

So I have done some searching and reading through the forums - what I'm having doesn't seem the be the normal DI "tick". And the other threads that might be having the same thing didn't seem to have a definitive cause - people where going to take their cars in and the threads then trailed off.

So when the car is in 4 cylinder mode she will have this rattle coming from up front (can't tell engine or exhaust) about half the time. It doesn't happen when she is switching into or out of 4 cylinder mode and it doesn't happen in 8 cylinder mode. It's not all the time in 4 cylinder mode either but consist enough and getting louder that I'll be calling them to schedule the appointment to bring it in next week. I'm just hoping some people here have some ideas before I deal with the dealership.

I captured a video with the pdr where you can hear it.
So you don't have to watch the entire video - you can hear it at the following points:
3:37-3:40
5:31-5:35
6:54
7:33-7:36
10:40-10:48
10:55-10:57
11:05-10:07
11:45-12:10
14:19-14:21

(car is 2015 z51 automatic)

tblu92

Very hard to hear but I do hear something-----REMEMBER when running in 4 cyl mode there are a set of butterfly valves in the exhaust pipes that almost completely close to eliminate the exhaust drone while running on 4 cyl-----These butterfly exhaust valves tend to chatter on occasion opening and closing rapidly which will create a metallic sound---
When I 1st got my C7 the valves were actually stuck closed all the time---on 4 cyl--I had to take the car immediately back to the dealer and they told me the were just "new" and sticking" Who knows what the real cause was-----
Most C7 owners wil simply have a tuner turn OFF the AFM system and be done with all the AFM issues---My mileage did not suffer much at all when I turned the AFM off---It's a sports/muscle car----not a Prieous------------

BYYEEEE

I had that noise and it ended up being the idler pulley! Dealer replaced it problem gone..it drove me crazy because everytime it was in V8 mode it would not do it. I even installed a AFM disable on my car to get rid of the noise. However when i got time i took it in.

NSC5

There was a problem with quite a few of the 2014 production year models where the damping fluid in the belt tensioner leaked out creating a noise particularly evident during V4 mode. The tensioner still functioned but was noisy because of the lost damping fluid which allowed it to rattle. I thought the issue was addressed during model year 2014 however even with a revised design some parts just fail so that could be the issue with your 2015. As suggested above the AFM sound control valves in the exhaust system could also be the issue.

BYYEEEE

Yea well i had this problem with the belt tensioner pulley on my 2015, 08/15 production date.

Kenafin

Took a little bit until I had a free day in my schedule to get the car in but dropped the car off yesterday and just heard back - tensioner pulley. (4/15 production date).

Rich0071

This rattle is what I'm hearing on my 2014 stingray with 29,500 miles. It's been doing it since 22,000 miles. The first dealer visit at 24,000 couldn't replicate the noise. It then took my quite a while to notice it was doing it in the v4 mode as it looked liked it was more related to going from 1400 rpm to 1500 rpm and appeared to be the differential noise that has got a lot of comments in the "warble' thread. My second visit on this issue was yesterday and the dealer recommended replacing the Delco belt with a Gates belt per a GM bulletin. Non warranty issue and $300. The belt is on order. I'm going to share this with the dealer to see what they have to say.

Rich0071

Update. The GM drive belt has been replaced with a Gates drive belt. Metal sounding noises and vibrations due to harmonics is now gone.

2lazy2type

Does it sound like the noise is coming from the dashboard?
I have a 2014 vette and I have an annoying rattle.
It sounds like it is coming from the passenger dashboard area.

I thought it might be a speaker shaking or something like that.

Thank you if you have a chance to respond.

Rich0071

With the windows up it sounds like it's coming from the dash. With windows down it sounds like it's coming from the drivers side body. Really can't tell exactly where the nose is coming from. If it's a harmonic issue noise can be created from one area and cause noises elsewhere. My noise is back. Went back to the dealer. They are scratching their heads. and "researching".
Waiting over a month to hear back from them.

2lazy2type

I wonder if we should just accept it at this point.

As a cure i'm thinking to get most of the inside dynomatted. Something like what DSOMonster did.
https://www.corvetteforum.com/forums...amn-place.html
I did notice that I can get the noise to go pretty steady if I put it in manual mode and keep the RPMs low.

jwmgr8

Please provide GM Bulletin related to fix?
Thanks

jwmgr8

I have had this problem since having the oil changed in my 2016 Z51
The noise occurs only in 4V under a slight acc. load. Does not occur in 8V mode period or in 4V mode if car is coasting??
Sound like butterfly valve flutter or as some say belt tensioner???

Does anyone have a GM TSB for this condition?

Thanks

jwmgr8

Dealer replaced Belt tensioner. Drive home it appears to have fixed this issue??? will know more after longer drives tomorrow.

ajcarson11

My car makes a fluttering sound when I apply slight throttle while In v4 mode only. It sounds like a mouse squeaking over and over and has a wind/woosh/air-rushing sound mixed in. As soon as the car goes back into v8 the noise goes away. I was under the impression that this is normal (just a characteristic of the engine sound with AFM valves closed). Are you suggesting that this is not normal?

Blue Curvette

Does the rattle sound like pre-detonation?

jwmgr8

Replacing Belt Tensioner Fixed V4 Rattle!
Really can not tell when AFM shifts from V8 to V4. Or back!

howe2011

FYI, you can't feel it but the power train sure does, when in V4 mode there is much vibration which has caused numerous front torque shaft bearings to fail. If the dealership can't figure out the noise issue, mention the torque tube front bearing. AFM is horrible for our cars. Its just a marketing scam by GM. Have it disable ASAP. Either with a AFM range delete or a tune.

Rich0071

Same problem, replacing tensioner fixed my rattle. I posted this on another thread. My rattle occurred at 1500 rpm going from V8 to V4. Dealer previously said it was the belt and replaced it for $300.

Kracka

You need a new belt + tensioner. Easy job. I did mine last spring.