Rumble Noise when in tow haul mode

[Demarsico]

Hello everyone. My first time here. I have a 2021 Sierra AT4 with the 6.2L. I have started to notice a noise when towing our boat that weighs about 6,000lbs. Several times during the trip to and from the lake I hear a rumbling sound that last like 2-4 sec. almost sounds like it can be a jake brake or hitting rumble strips on road. I hit no strips. I can’t recall if it happens on downshift or what. But it does concern me. I drove home from work today with our towing and put it in tow haul mode. It made the noise 3 times in 45 min drive. Any ideas what I’m dealing with? Would it be a bad clutch issue or is this normal?  I do have the performance GM installed exhaust and performance GM installed air intake. I called dealer today and they said bring it by and they MIGHT have time to get to it next week. I planned to hit the lake this weekend for Labor Day. Thanks. 

[bigdoug42]

Sounds like you have torque converter clutch chatter, I had that with my T1 2019 Z71 with the 5.3 and 8 spd. There is a TSB with points out that the issue is the trans was filled with old stock trans fluid which attracted moisture and caused the fluid additives to degrade. The fix is to take it to the dealership and they will scope it while driving and then flush the trans and add new full synthetic Mobil1 fluid. Took care of mine, no further issues. You however have a 2021 with the 10 spd I am guessing, but it sure does sound like the same issue.

Maybe one of the far more knowledgeable people on here can help you out more.

 

Good Luck!

Edited September 6, 2021 by bigdoug42