2021Yukon/ Intermittent rattle under truck at low speeds

[paspasero]

I’m also suspecting the torque converter to be an issue. One other issue I reported and forgot to mention was shifting between gears under load (such as going up a hill) is getting harsh. You feel a slight jerk after every gear change.

 

[MobileHomie]

Thanks for your input Thrust! So the dealer had the truck for three days and had two of their top technicians watch the video and inspect the truck while it’s on a lift. They took it for a test drive and claimed they didn’t hear anything out of the ordinary. Apparently, my video was not enough to motivate them to keep looking for the root cause so they requested I pick it up. Quick disclosure, my truck had three valve lifters replaced at 13k miles. My family and I were stranded 6 hours away from home. I’m curious if the exhaust manifold were not torqued to specs. One other issue we are having is the smell of exhaust in the cab with all the windows closed and vent set to recirculate. The dealer’s solution for the exhaust smell was to change the air filter. SMH. I do all the work on our vehicles and frustrated with my Yukon because it’s still under warranty and I have no choice but to have the dealer fix it. Thanks again for replying!

The exhaust smell inside the cabin is a problem! Most likely broken exhaust manifold bolts. Mine had an exhaust smell too, it stopped after a cam swap (heads removed)
HIghly suspect that the noise coincides with the cylinder deactivation.
GM was playing with that cylinder deactivation crap back in the '90s with the old Northstar engines, hasn't gotten any better.
High performance engines need a solid valve train, not tender bits prone to failure.

 

[B-train]

I'm going to go with the DFM system. The noise starts and the exhaust shakes - it appears to be pressure related in the system. You can kind of see the pulses coicide with the noise. If go with loose/broken manifold bolts, some exhaust mount installed incorrectly, a heat shield too close, etc first. Easy to look at. If that's not the case, maybe a bad catalyst? Rattling inside the chamber when cylinders are dropped and pressures change? Or maybe something isn't right with the replaced lifters and DFM activation?

 

[paspasero]

The exhaust smell inside the cabin is a problem! Most likely broken exhaust manifold bolts. Mine had an exhaust smell too, it stopped after a cam swap (heads removed)
HIghly suspect that the noise coincides with the cylinder deactivation.
GM was playing with that cylinder deactivation crap back in the '90s with the old Northstar engines, hasn't gotten any better.
High performance engines need a solid valve train, not tender bits prone to failure.

I’d say I’m loving the fuel economy of my 5.3L but it’s not worth it if my family and I may get stranded far from home again.

 

[paspasero]

I'm going to go with the DFM system. The noise starts and the exhaust shakes - it appears to be pressure related in the system. You can kind of see the pulses coicide with the noise. If go with loose/broken manifold bolts, some exhaust mount installed incorrectly, a heat shield too close, etc first. Easy to look at. If that's not the case, maybe a bad catalyst? Rattling inside the chamber when cylinders are dropped and pressures change? Or maybe something isn't right with the replaced lifters and DFM activation?

Now if I could just get the dealer to use their high tech troubleshooting tools and prove that ignition timing, fuel ratio, power bands, etc are still within spec. I’m under the impression that I can only take something completely and obviously broken to them for repair and not something that’s about to break and needs preventive maintenance.

 

[MobileHomie]

I’d say I’m loving the fuel economy of my 5.3L but it’s not worth it if my family and I may get stranded far from home again.

I hear you!
My '17 GMC with 6.2L was out of warranty when a collapsed lifter bent a pushrod. I opted for an AFM delete cam swap. Yesterday I took my wife and daughter to a holiday symphony in Reno, 328 miles round trip and 18 MPH with the cruise set at 87MPH.

I have an aunt and uncle that has a 5.3L truck that is under warranty and insist GM does their due diligence. Warranties are inherently a pain in the ass where the warrantor hopes the warrantied just give up.

 

[paspasero]

I hear you!
My '17 GMC with 6.2L was out of warranty when a collapsed lifter bent a pushrod. I opted for an AFM delete cam swap. Yesterday I took my wife and daughter to a holiday symphony in Reno, 328 miles round trip and 18 MPH with the cruise set at 87MPH.

I have an aunt and uncle that has a 5.3L truck that is under warranty and insist GM does their due diligence. Warranties are inherently a pain in the ass where the warrantor hopes the warrantied just give up.

Yes! If I don’t sell my truck by the time my warranty expires, I will definitely switch back to a reliable gas guzzler!

 

[paspasero]

My big baby. Would hate to let her go over reliability issues.

 

[iamlegion]

Hey, created an account just to share I think I know what your issue is if you haven't solved this.

Take a strong thick zip tie or metal hose clamp. Before and after your muffler there will be two valves with springs wrapped around them that you can grab and rotate open/closed. These are designed to attenuate the AFM pulses but can rattle (think if someone opened a large soup can lid 99% of the way then shook the can, the lid will flap against the can in certain scenarios).

If you want to isolate it, look carefully and figure out which way to rotate them to leave them open, hold it there then wrap the zip tie or hose clamp around it then tighten it to lock them open. When you do a test drive if you locked them closed you'll know, but if you lock them open and this was the problem the rattle should be gone and when it switches to AFM you'll hear a "helicopter in the distance" sort of chop/drone more pronounced.

I'm about to swap my whole system out for the GMPP system, and I'd offer you mine to replace yours if that's it but I have an XL so I think it won't fit if you're the shorter wheelbase.

 

[bradac]

Omg my 2021 suburban has the EXACT same issue as your car. I replaced the “front muffler” which is the park from the flex pipe to the muffler in the center, this includes the flapper. My flapper was rattling, it fix the flapper rattle but still have a vibration near the engine, I think it’s exhaust manifold I had my lifters replaced at 15k miles, this rattle noise has been going on for about 10k miles way worst in the summer.