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2021 AT4 Noise Driving Me Insane


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I have a 2021 AT4 6.2L that I had the dealer install the GM Performance exhaust. At first everything was fine, but I am now hear a metallic flapping / screeching sound every time the truck comes out of auto stop/start, when I am slowing down to a stop and the truck downshifts, and occasionally at cruising speeds when the gas pedal is feathered. It is a brief noise that doesn't last long but is still like listening to nails on a chalkboard. It is loudest when slowing down to a stop when backpressure from the transmission downshifting releases. It sounds similar to issues people have had with the adaptive exhaust valves, but the performance exhaust eliminates those (unless they go internal with the performance exhaust similar to Ram). I uploaded a couple of youtube videos trying to capture the sound. If you listen carefully you can hear the noise right after the engine turns over:

 

 

 

I took it to the dealer who installed the exhaust and was quickly discredited. They said it was the starter and claimed they could not hear it at any other times. 

 

- Could this actually be the starter? It doesn't make the noise during a cold start, only when the auto stop/start reengages.

- Could it be something with the performance exhaust? Are there adaptive valves internal to the muffler?

- Has anyone come across anything like this in the past?

 

Any insight would be greatly appreciated as I don't know how much longer I can withstand this subtle torture. 

Edited by LionSeal
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I have a 2021 AT4 6.2L that I had the dealer install the GM Performance exhaust. At first everything was fine, but I am now hear a metallic flapping / screeching sound every time the truck comes out of auto stop/start, when I am slowing down to a stop and the truck downshifts, and occasionally at cruising speeds when the gas pedal is feathered. It is a brief noise that doesn't last long but is still like listening to nails on a chalkboard. It is loudest when slowing down to a stop when backpressure from the transmission downshifting releases. It sounds similar to issues people have had with the adaptive exhaust valves, but the performance exhaust eliminates those (unless they go internal with the performance exhaust similar to Ram). I uploaded a couple of youtube videos trying to capture the sound. If you listen carefully you can hear the noise right after the engine turns over:
 
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I took it to the dealer who installed the exhaust and was quickly discredited. They said it was the starter and claimed they could not hear it at any other times. 
 
- Could this actually be the starter? It doesn't make the noise during a cold start, only when the auto stop/start reengages.
- Could it be something with the performance exhaust? Are there adaptive valves internal to the muffler?
- Has anyone come across anything like this in the past?
 
Any insight would be greatly appreciated as I don't know how much longer I can withstand this subtle torture. 

I understand you can turn the stop start off I’d start there.


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15 minutes ago, lebag335 said:

Might be lose heat shielding..

That was one of my initial thoughts as well as I have had heat shield issues on previous vehicles. I shook everything that I could shake and verified all bolts were tight and it's still making the noise.

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I have a  2021 TB with a 6.2 and have read several threads in these forums about it.  Seems like its something that happens with varying degrees on all 6.2s.  The belief I have after reading and doing some testing is that it has something to do with DFM.  People have tried addressing it as a starter issue, exhaust issue, flapper issue, etc with no success.

 

These noises don't happen (on mine at least) when you override the system by putting your gear shifter down to L, and switching to gear 9 - drive around and check it out for yourself.  I plan on purchasing a Pulsar LT when they are available again.

 

 

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My 6.2 makes this noise when started first thing in the morning and also under acceleration between 1,000 and 2,000 RPM.  Took it to the dealer and of course they say it is normal.  I believe it may be the high pressure fuel system.  They basically told me if there are no CEL lights and nothing evidently wrong I had to live with it.  It drives me insane on an over 60K truck every time I drive it.  Add that to the out of alignment bed and I am not happy at all with this purchase.

Edited by Troger
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Loose oxygen sensor I bet. Either loose in its casing, or loose in threads. At startup, the exhaust shakes it a bit. Once the truck is running, the flow keeps it pinned. 
Could also be the cat weld broken loose internally. Maybe try hitting the exhaust in different spots, but with a rubber mallet. 

just a guess.

Edited by Sqrls
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Perhaps an exhaust leak somewhere that whistles/emits the noise when the exhaust is warm/hot and there is a surge in exhaust flow -- like when auto stop/start restarts, or a downshift increase revs?

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