Turtlern56

12,000 miles on my 2020 AT4 HD now and it knocks just as loud as ever. Still quiet upon cold start as it was when new then comes on strong and loud. There are very few instances when engine is warm and idling I wont hear it. I still can’t tell exactly what it is. Seems quieter when clutch fan cycles slightly but also could just muffle it a bit to my hearing. Still frustrating as all get out to me. I can hear it over the radio at low volume in closed cab. Just thought I would give my update. I still follow this thread hoping some day somebody finds the fix.

Today I seen another 2020 Denali in an empty parking lot and I parked about 3 spots away. Turned my truck off cracked the windows and it was running. We could hear same knock on that truck but wasn’t terrible loud but even my kids could distinguish the sound. I agree on the air thumping sounds (Compressor like) Especially sitting in the truck with the door open or window cracked. My truck now has 1000 miles on it. In the mornings with a cold remote start it will do the same knock for a split second Just Enough for 2-3 knocks then quiets down for a minute or two then comes on strong. Once the truck has been running for 5-10 mins it knocks obnoxiously loud. Driving us crazy! 500-1300 rpms or so it’s very audible. Knock knock knock knock I hear it in my sleep. Lol

I have a 2020 AT4 HD 400 miles now and mine has made that exact same knock as the video outlines. I commented to the salesman about it but he said he wasn’t that familiar with any of the sounds. I had been waiting a month for delivery bc of the GM strike. I went back to the dealer the same day I took delivery last week and made them start another diesel and it had same knock but not near as loud as mine. Heard three others since with no noise. It’s Horrible at idle and seems to go away about 900-1000 rpms. Some mornings not audible for a minute or two then comes on strong as it warms. Service manager today says it’s normal and they printed me off the ticking service bulletin. It’s a knock not a tick. He also told me to drive it and about halfway through oil life if still audible then they might investigate it. It’s a little embarrassing I’ve had a couple people ask me “what’s that knocking?” I give them the $70k shrug and say it’s normal. Lol. I hope they figure something out. Reprogram an injector if it’s like a fuel knock or something. Found this thread researching and thought I would chime in.