Exhaust Rattle on 2021 6.2l CC

burgie189 · February 18, 2021

Hi Everyone,

Looking for some feedback on if anyone else is having what sounds to me, like a rattle from the exhaust on the passenger side near the rear wheel. Mostly hear it at low to stopped speeds and mostly when in gear. Occasionally, it will happen in park while idling but not reliably enough to get under and check it out.

Troger · February 18, 2021

I have a rattle sound under light acceleration between 1-1.5K rpm. Not sure if this is like yours.

Not my video but sounds just like my truck, a 2021 6.2L (Turn up volume to hear it). It's driving me nuts especially on a new expensive vehicle.

Wakinvol · February 22, 2021

Check where the exhaust pipe goes into the back side of the chrome tip. I bet that's where it's coming from.

OnTheReel · February 22, 2021

That’s my 2016 in the video above. It was the flapper making that terrible noise.

Kent Hagler · February 23, 2021

On 2/18/2021 at 9:13 AM, burgie189 said:

Hi Everyone,

Looking for some feedback on if anyone else is having what sounds to me, like a rattle from the exhaust on the passenger side near the rear wheel. Mostly hear it at low to stopped speeds and mostly when in gear. Occasionally, it will happen in park while idling but not reliably enough to get under and check it out.

I had a 2021 come in the shop with the same concern. The spare tire shield was slightly bent and contacting the exhaust pipe intermittently. Crawl under and look just above the rear axle in that area. Pry bar fixed it.

burgie189 · February 23, 2021

13 hours ago, Wakinvol said:

Check where the exhaust pipe goes into the back side of the chrome tip. I bet that's where it's coming from.

Thanks! I'll check it out.

burgie189 · February 23, 2021

3 hours ago, Kent Hagler said:

I had a 2021 come in the shop with the same concern. The spare tire shield was slightly bent and contacting the exhaust pipe intermittently. Crawl under and look just above the rear axle in that area. Pry bar fixed it.

I'll check this too! Thanks

Jarid Ashman · July 21, 2021

On 2/22/2021 at 11:28 AM, OnTheReel said:

That’s my 2016 in the video above. It was the flapper making that terrible noise.

DUDE !!!! You’re a life saver for this!! I’m having the same exact exhaust noise issue!!! 2021 Trail Boss 3200k Miles and it’s a flapper… just took it back to dealer and they said they can’t hear anything which is total bullshit. What’d you do to fix the flapper?

WeGone · July 21, 2021

If your not one to have it removed, Turn it so its open and put a clamp around it.

Do a search lots of posts on it.

OnTheReel · July 21, 2021

3 hours ago, Jarid Ashman said:

DUDE !!!! You’re a life saver for this!! I’m having the same exact exhaust noise issue!!! 2021 Trail Boss 3200k Miles and it’s a flapper… just took it back to dealer and they said they can’t hear anything which is total bullshit. What’d you do to fix the flapper?

Traded the truck. And put a catback on the new one. Even if they replace the flapper(s) it’ll make the noise again before too long. And even if clamped open, it still blocks off like a third of the pipe so there’s a bit of performance to be gained getting rid of it altogether.

Jarid Ashman · July 24, 2021

On 7/21/2021 at 7:33 PM, OnTheReel said:

Traded the truck. And put a catback on the new one. Even if they replace the flapper(s) it’ll make the noise again before too long. And even if clamped open, it still blocks off like a third of the pipe so there’s a bit of performance to be gained getting rid of it altogether.

OnTheReel, I know you had mentioned you traded your vehicle out with issue. But when the issue was present did it sound as though it was coming from the front end or could you distinctly tell it was coming from back? My 2021 Trail Boss only has 1 flapper toward the back passengers side right before muffler. Though my issue sounds like it's coming from front end by cats/manifold

rsimons · August 31, 2021

I have the same problem on my 2021 6.2L Sierra Denali. 1st time I took it to the dealer they said it was the flapper valve and it was normal. I then installed a Magnaflow cat back, but it still does it. Took it back to the dealer and they said they drove another one that made the same noise so it's normal. I asked what it was and they said they don't know. It sounds like an exhaust leak, but they said there where no leaks. It does it bad at cold start, and also on decel, right before you come to a stop. Also, sometimes on light acceleration.

Hkb82 · August 31, 2021

My 2021 at4 6.2lL with 3200km also makes this sound when stopping and at light throttle. I’ve been in to the dealer a few times now and it seems to be a normal sound they at. I can’t believe it is supposed to make this sound. I put a dorks cat back on amd it’s actually more pronounced at stop signs. I think it’s the dfm system. I’m super on the fence about getting a pulsar LT to try and see if killing the dfm also kills the noise.

migmowner · September 1, 2021

my 2017 5.3l had the rattle also, it would rattle when the AFM would run in 4 cyl and you were on the gas but not enough to switch back to 8 cyl. i removed the flapper valve and never looked back. that was 30,000 miles ago. i had a 2015 5.3l that never had this issue, only difference was on the 2015 the flapper was in front of the muffler, on the 2017 it is after the muffler

Edited September 1, 2021 by migmowner

Hkb82 · September 2, 2021

My dealer also thought it was the flapper so they warrantied and replaced the entire exhaust. No change I put the borla on eliminating the flappers but still got it. So it’s either the cats or maybe the heat shield on the o2 sensor in front of the cats. I truly think it’s the dfm.