I have a 2008 GMC sierra 2500 HD. When I stop at a light in park can here a faint whine behind the dash. The sound goes away as soon as I accelerate. If I switch to neutral the sound almost goes away. Anyone have any ideas. My thoughts were hydroboost, power steering pump, transmission, for some reason I think Its the alternator. Anyone have any ideas?

 

It's really tough to say. You can remove the serpentine belt and start the truck and see if the noise is still there or gone. That'll rule in or out p/s pump, and alternator. If noise is still there you are probably looking at possible trans pump/converter.

 

Just a thought, but might also check the air intake make sure everything is snug and secure... you'd think an air or vacuum leak would cause some driveability issues but its something to rule out....