Hey all, my Tahoe has been making an awfull noise when it starts up when the car is all warmed up. It won't do it on a cold start or if the trans temp is less than about 130. Above that when it starts or is starting up the engine coming out of auto-stop it makes a really bad noise. It's kind of like a groaning/grinding combination from the transmission. Since this started I have had the jerky start and jerky braking into auto-stop each. As far as I know the car is up to date on programming, and this is something that recently popped up (since the dealer replaced the trans fluid pressure regulator spring for slipping in gear).
Has anyone had something like this happen that I can point the dealer into the right direction? Unless it's a hybrid part I'm out of warranty, so I'd rather have it pretty much diagnosed before spending too much to fix it.

 

I get a whining noise sometimes from the auxiliary pump when I am in Autostop mode, just behind the brake paddel. you can hear it loud from the outside of vehicle.
once the engine starts the noise disappears.
Thats teh only sound I get ocasionaly

 

I know that this is an old post.. but I was searching for similar issues and this came up! Did you find out what was going on? Mine is doing pretty much the exact same thing.. I am assuming that its related to the AUX Transmission Pump.. which I just ordered replacement parts and looking to get it swapped out soon. I have had that groaning/grinding noise at low speeds in low gears.. and then I started experiencing what felt like a buck/slip.. My theory is that the AUX pump isn't providing the power/pressure that the transmission needs and is causing those sounds.. and then on bad occasions just freaks out completely (causing the buck/sip feel)

I am hoping that replacing the pump will fix both those issues for me!

 

Doubt if the OP will be back, it looks like he got rid of his Hybrid 4-12-2012 by his last post. The worst thing about having one of these GM Hybrid TwoMode vehicles is the total lack of expertise out in the market place.
I see nothing wrong with raising a dead thread, maybe someone has solved the issue and can chime in.