Low mileage Underbody/Exterior rattle at idle, not suspension

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StevenJay
Posts: 60
Joined: Sat Oct 28, 2017 10:43 pm
Location: Lake County Illinois

Low mileage Underbody/Exterior rattle at idle, not suspension

Post by StevenJay »

I have a constant rattle at idle and above rpms that I'm almost positive is exhaust related. Its a 2014 with 14,000 miles and is in like new condition (besides the dam rattle) I've checked if any heat shields are contacting the exhaust and all are clear. Im going to put it up on ramps to find the exact spot where its coming from. I thought I'd see if anyone else has come across and fixed a similar issue. Exhaust is stock, all hangers in great shape.
Steven J.
-2014 Chevy Caprice PPV Pre-Production Pilot vehicle RPO code-Switchblade silver metallic purchased 11/2017
-2017 Chevy Caprice PPV- Switchblade silver metallic-GM Show Car RPO code. purchased 1/2018
s/c'd cav
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Joined: Mon May 30, 2016 3:12 am
Location: PHOENIX AZ

Re: Low mileage Underbody/Exterior rattle at idle, not suspension

Post by s/c'd cav »

my 14 with 14k on it , is whisper quiet
CrashTestDummy
Posts: 2300
Joined: Sat Feb 07, 2015 2:31 pm
Location: Pearland, Texas

Re: Low mileage Underbody/Exterior rattle at idle, not suspension

Post by CrashTestDummy »

There's a seam where they welded the 'can' of the muffler together that runs the length of the muffler on the top, against the body. I was surprised at the mufflers on our '12 that the seams were starting to corrode. The car did enjoy it's service life on the highways of Wisconsin, so the salt air probably contributed to that, but it looked like one side was actually leaking some.

Had a friend with a Mustang that had those seams come apart, and the car sounded like someone was playing a steel drum under the car. It was a C Prepared autocross car, so it wasn't very quiet to begin with, but new mufflers made a lot of rattling go away.

See if you can reach your hand up and run it along the top middle of the muffler and see if it's split.

Otherwise, when you get it in the air, run your hand along the entire exhaust system and see if one of the heat shields is bent. I seem to remember reading here where on certain years the exhaust system heat shields would flex away from the body at pursuit speeds and sometimes permanently bending and laying against the exhaust system.
Gene Beaird,
Pearland, Texas
2012 Caprice 9C1
1992 B4C 1LE Camaro
2018 Tahoe PPV (her car)
1995 DGGM Impala SS
1985 Firebird - 310 LS1 C Prepared autocross car.
1980 Bluebird Wanderlodge
And some others
Do YOU have my SPID?
StevenJay
Posts: 60
Joined: Sat Oct 28, 2017 10:43 pm
Location: Lake County Illinois

Re: Low mileage Underbody/Exterior rattle at idle, not suspension

Post by StevenJay »

Thank you for the Info Gene, I appreciate it!
Steven J.
-2014 Chevy Caprice PPV Pre-Production Pilot vehicle RPO code-Switchblade silver metallic purchased 11/2017
-2017 Chevy Caprice PPV- Switchblade silver metallic-GM Show Car RPO code. purchased 1/2018
StevenJay
Posts: 60
Joined: Sat Oct 28, 2017 10:43 pm
Location: Lake County Illinois

Re: Low mileage Underbody/Exterior rattle at idle, not suspension

Post by StevenJay »

Was under the car with it on jackstands and can replicate the sound by tapping on the mid/crossover ehxaust assembly. No interference with transmission brace or the second tunnel brace more towards the rear. I checked the top of the mufflers and theres no splitting on the top. Watching videos of loose or broken baffles in the exhaust is the exact same noise! Obviously no TSBs for the Caprice but when looking at similar issues (on similar vehicles) found the Camaro had an exhaust baffle issue that also made an underbody rattle. Now to just isolate whether its a resonator or the actual muffler at the rear so I know which part is the culprit. Luckily on the Caprice, we are able to unbolt the rear muffler from the mid exhaust/crossover...the Camaro is all one piece from the cats back. (atleast the years I was looking at)
Steven J.
-2014 Chevy Caprice PPV Pre-Production Pilot vehicle RPO code-Switchblade silver metallic purchased 11/2017
-2017 Chevy Caprice PPV- Switchblade silver metallic-GM Show Car RPO code. purchased 1/2018
StevenJay
Posts: 60
Joined: Sat Oct 28, 2017 10:43 pm
Location: Lake County Illinois

Re: Low mileage Underbody/Exterior rattle at idle, not suspension

Post by StevenJay »

Just to help any other people that come across this post having a similar rattle. It was one of the resonators right behind the converters that is attached to the exhaust mid section or crossover section as GM calls it. Weirdly enough I could replicate the noise with my hand balled up in a fist and pounding on the resonator more than I could with a rubber mallet. No visible clues when looking at it from outside; its definitely a baffle that came loose inside. Replaced the mid/crossover exhaust section, which was not cheap!!
Wire brushed all mating surfaces, installed new donut sealing rings (on both sides) along with new (prevailing torque) nuts for the connections to both converter pipes. Also used new sealing gaskets on the rear connections to both right and left mufflers/tailpipe assemblies to ensure I would not have any leaks once finished. Followed the service manual exactly which also included anti seize on the rear tailpipe to mid section bolts. Annoying rattle gone!!
Steven J.
-2014 Chevy Caprice PPV Pre-Production Pilot vehicle RPO code-Switchblade silver metallic purchased 11/2017
-2017 Chevy Caprice PPV- Switchblade silver metallic-GM Show Car RPO code. purchased 1/2018
CrashTestDummy
Posts: 2300
Joined: Sat Feb 07, 2015 2:31 pm
Location: Pearland, Texas

Re: Low mileage Underbody/Exterior rattle at idle, not suspension

Post by CrashTestDummy »

StevenJay wrote: Tue Sep 08, 2020 10:52 am <SNIP>Followed the service manual exactly which also included anti seize on the rear tailpipe to mid section bolts. Annoying rattle gone!!
Congrats on the success! I think we have an aftermarket cat on our 92 B4C 1LE Camaro that has a broken matrix. Luckily, it isn't as much a PITA newer cars are about any little thing exhaust-wise, but a rattle, just the same. When we get done wht our SVO restomods, the Camaro goes up, and I may pull the cats and clean them out, since the car is now an antique.

I quoted your reply above, because I can tell you for certain that they don't use anti-sieze at the factory. That must be a service recommendation, since those fasteners rust out so badly. Had to take a sawsall to one of the bolts, and another just broke when I was pulling the OEM exhaust.
Gene Beaird,
Pearland, Texas
2012 Caprice 9C1
1992 B4C 1LE Camaro
2018 Tahoe PPV (her car)
1995 DGGM Impala SS
1985 Firebird - 310 LS1 C Prepared autocross car.
1980 Bluebird Wanderlodge
And some others
Do YOU have my SPID?
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