Thought I would put it out there: just got my 2012 yukon denali hybrid back from the shop, to diagnose & repair a loud whine when after a long drive when the truck was fully warmed up & the engine went into auto-stop. Took a week for dealer to replicate the issue long enough to pinpoint the noise, but the transmission cooler bypass valve (or line, they're not sure which) was making a racket when the auxiliary transmission pump would run after being fully warmed up. Sounded like a hydraulic pump cavitating. Pop the hood, the ice starts & the noise instantly disappears because the transmission is using the engine to pump.

Very hard to pinpoint, but very happy with Ryan chev in Buffalo, mn for sticking with it to figure it out.

 

Did anyone come up with a solution to this issue? I just posted about the issue being related to the transmission fluid cooler bypass, but after driving it today it turns out they didn't get it fixed.

 

If it is the noise in the video I posted long ago, only fix is very expensive. Front pump housing in trans, or whole trans.


It causes no harm. Goes away as weather changes. But comes back when conditions are right.

 

Mine has done this since it was new, comes and goes, no rhyme or reason, usually after driving it if I leave it running and jump out and it drops into autostop. Doesn't seem to have any harmful effects except for the noise. I always assumed it was the HVAC. Incidentally, I had the auxiliary Transmission pump replaced long ago for a different reason and it didn't change.