funny knocking sound
Thread Starter
Racer
Joined: Jan 2009
Posts: 279
Likes: 1
From: North Port Florida
funny knocking sound
I've noticed that after cranking the car and it idles I'm hearing a rattle or knocking sound that seems to be coming from under the car. It does not sound like an engine knock, but more like a dull metal thud...I figure it may be the exhaust pipe tapping against another fixed object?
In neutral (or in gear with clutch in) I've hit the throttle to see if the noise stops or increases/decreases with RPMs. It doesn't seem to do either, although it is not heard under throttle...it's probably there, but the engine noise drowns it out. This sound remains even after short trips, longer trips, and casual driving or spirited driving. It's noticeable in the car as well as outside the car.
Anyway, I do not have access to a lift or ramps so I can't crawl underneath to see what the source is. Anyone else experience this? It's a 2003 Z with 17,500 miles, and is completely stock. It's a relatively new discovery so I'm guessing something has worked itself loose?
In neutral (or in gear with clutch in) I've hit the throttle to see if the noise stops or increases/decreases with RPMs. It doesn't seem to do either, although it is not heard under throttle...it's probably there, but the engine noise drowns it out. This sound remains even after short trips, longer trips, and casual driving or spirited driving. It's noticeable in the car as well as outside the car.
Anyway, I do not have access to a lift or ramps so I can't crawl underneath to see what the source is. Anyone else experience this? It's a 2003 Z with 17,500 miles, and is completely stock. It's a relatively new discovery so I'm guessing something has worked itself loose?
Le Mans Master
Joined: Oct 2007
Posts: 6,868
Likes: 770
From: Kelso Washington
St. Jude Donor '09, '13, '15
Sounds like you are going to HAVE to get underneath it to hear where it is coming from.
You can get a floor jack and two floor stand set for well under fifty bucks. Even if you only get it up far enough for what I propose.
Cut up an old garden hose so you have about a three or more foot length. Hold one end to your ear and use the other end to wander around underneath until you hear the knock. It's an old-school technique that works for all kinds of trouble-shooting. It'll tell you exactly where the knock is coming from.
You can get a floor jack and two floor stand set for well under fifty bucks. Even if you only get it up far enough for what I propose.
Cut up an old garden hose so you have about a three or more foot length. Hold one end to your ear and use the other end to wander around underneath until you hear the knock. It's an old-school technique that works for all kinds of trouble-shooting. It'll tell you exactly where the knock is coming from.
Tech Contributor
Joined: Dec 2006
Posts: 10,962
Likes: 29
From: Van Buren Arkansas
Wounded Warrior Escort '11
I agree too. You really need to get under there. Buy a set of ramps or take it to someone with a lift that you can park it on briefly to get a listen under there.
Thread Starter
Racer
Joined: Jan 2009
Posts: 279
Likes: 1
From: North Port Florida
I'd like to say yes, but no. The most recent trip I took in the car was just 12 miles, but it's a 30+ minute drive due to traffic. It was the same as when it was started. It's far more noticeable while the car is in the garage due to the tight space. Very frustrating that I'm not able to get under there any time soon.... The hose idea is my next best bet until I get some time. Keep the suggestions coming, please!
Thread Starter
Racer
Joined: Jan 2009
Posts: 279
Likes: 1
From: North Port Florida
update...
I cranked her up again this afternoon to give it a closer listen. While sitting in the car with door open and car out of gear, I gave progressive application to gas pedal while I held my head outside of car cabin. It DOES seem that the rattle increases speed with throttle application, but is faint and harder to hear with engine noise. Someone suggested the torgue tube may be going...not sure. Haven't noticed any performance problems so can't shed much more light than this...
Burning Brakes
Joined: Jun 2007
Posts: 1,047
Likes: 69
From: Hanover MA.
I cranked her up again this afternoon to give it a closer listen. While sitting in the car with door open and car out of gear, I gave progressive application to gas pedal while I held my head outside of car cabin. It DOES seem that the rattle increases speed with throttle application, but is faint and harder to hear with engine noise. Someone suggested the torgue tube may be going...not sure. Haven't noticed any performance problems so can't shed much more light than this...
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Melting Slicks
Joined: Oct 2001
Posts: 2,320
Likes: 2
From: Salem Oregon
Its a long shot but my 98 did pretty much the same thing.
It turned out my one of my cats fell apart inside, and was rattling around. It sure sounded like the engine or clutch setup was doing it. I found it by getting the car in the air to listen to it. Then tapped on the exhaust with a rubber hammer. I was relieved to say the least.
Good luck with it, Randy
It turned out my one of my cats fell apart inside, and was rattling around. It sure sounded like the engine or clutch setup was doing it. I found it by getting the car in the air to listen to it. Then tapped on the exhaust with a rubber hammer. I was relieved to say the least.
Good luck with it, Randy
Thread Starter
Racer
Joined: Jan 2009
Posts: 279
Likes: 1
From: North Port Florida
I *believe* both. I'll have to check again to be sure...
Is you car a 6 speed? If so, Does the noise go away with the clutch depressed?
It turned out my one of my cats fell apart inside, and was rattling around. It sure sounded like the engine or clutch setup was doing it. I found it by getting the car in the air to listen to it. Then tapped on the exhaust with a rubber hammer.
Bearings in your idler pulley. If that's it, it's a pretty easy fix. There should be many posts on it. Give it a search and see if that's the problem.
I'm still tellin' ya...the hose trick will pinpoint where the noise is. It works.
Race Director
Joined: Feb 2008
Posts: 17,336
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From: Maker of Sharp Objects, AL - Roll Tide
St. Jude Donor '10-'11-'12-'13-'14-'15-'16-'17
St. Jude Knife Maker
Is this the old "as soon as I crank my car up and start to drive it down the road I hear a clicking or knocking sound in the motor and as I drive it it goes away"?
I don't think this is what you are talking about but mine does this. It seems that many LS1's do it, and maybe some of the LS6's too. I crank my car up every morning and it sounds pretty rough. I back it out of the driveway, put it in first gear, and by the time I wind up 1st gear and shift to second the noise is gone. Usually takes about 100 ft until the noise disapears.
Weird, and doesn't sound right at all, but alot of people seem to have this issue.
I don't think this is what you are talking about but mine does this. It seems that many LS1's do it, and maybe some of the LS6's too. I crank my car up every morning and it sounds pretty rough. I back it out of the driveway, put it in first gear, and by the time I wind up 1st gear and shift to second the noise is gone. Usually takes about 100 ft until the noise disapears.
Weird, and doesn't sound right at all, but alot of people seem to have this issue.
Thread Starter
Racer
Joined: Jan 2009
Posts: 279
Likes: 1
From: North Port Florida
nope...not the same. based on the searches I've done so far it's leaning toward a broken weld in the exhaust or a cat going bad. won't know until I get her up in the air, tho.....
Thread Starter
Racer
Joined: Jan 2009
Posts: 279
Likes: 1
From: North Port Florida
nope...not the same. based on the searches I've done so far it's leaning toward a broken weld in the exhaust or a cat going bad. won't know until I get her up in the air, tho.....
Instructor
Joined: Aug 2007
Posts: 221
Likes: 8
From: Spartanburg SC
i know this may sound crazy but look at the clamps that hold your air filter in. i notice when i started my car the other day that there was a knocking or rattle of some sort anyway i open the hood sure enough both clamps that hold the airfilter on came lose. i still have no idea how they came lose because they are on there pretty good.
Thread Starter
Racer
Joined: Jan 2009
Posts: 279
Likes: 1
From: North Port Florida
...okay. After aout 30 minutes of trying to crawl under this car I was able to accomplish the following: I believe now more than before that my problem is a failing cat. Under acceleration it becomes harder to hear, but when the rpm's drop it becomes more noticeable. The sound seems to be strongest around the cats and it is like hearing a small piece of metal flopping around inside. I shook the crap outta the pipes to check for weld breaks/loose connections...no luck. The rattle/knocking sound is almost consistent under accel/decel, but a little delayed. If this is the cat, isn't the GM emmission warranty good for 7 years? If so, this could be a dealership fix I'd think? 
Oh, and the hose trick worked enough to get me to the cats and away from the tranny
Oh, and the hose trick worked enough to get me to the cats and away from the tranny
Last edited by KWIKSILVERZ; Feb 21, 2009 at 11:20 AM.
Safety Car
Joined: Oct 2003
Posts: 3,854
Likes: 8
From: Pearland, TX
Cruise-In VIII Veteran
St. Jude Donor '03 thru '20
I would agree that the cats are a likely suspect.
Emissions components have a longer warranty (I don't remember the time) but you could call the stealer to ask or I'm sure someone on here knows as well.
Emissions components have a longer warranty (I don't remember the time) but you could call the stealer to ask or I'm sure someone on here knows as well.
Thread Starter
Racer
Joined: Jan 2009
Posts: 279
Likes: 1
From: North Port Florida
I'll look in my car paperwork. Even though I'm the 2nd owner, I should still be covered if time hasn't lapsed. I'm thinking it's 7 years though...