Quick update: I removed the serpentine belt and inspected all the idlers and stuff - I did not hear or feel anything odd, a very faint whirring from the alternator but that may be normal... I put everything back together and started it up and best I can tell the whining noise is coming from the alternator area. One more thing, I have started getting a screeching noise occasionally and it usually happens on start up and when accelerating hard on the freeway. Best I can tell this only happens when the AC is running (a couple of times it has screeched when I turn it on). Could that be the alternator screeching when the load of the AC is put on it or could it be unrelated? Regardless, I think I will swap out the alternator and see if that fixes the whining. Any suggestions for a good replacement under 120? Rock Auto has a Remy 160amp for about $98 but I don't know anything about that manufacturer.

 

If you get a noise only when the AC is switched on, check the AC belt idler/tensioner. I'm assuming that your 2009 Tahoe has a separate small belt with an idler/tensioner for the AC compressor like my 2005 Yukon has.

 

Actually mine does not have an idler/tensioner, it uses a stretch belt. Supposedly you can install one if you want as the bolt holes are still there from previous models.

 

You can use a length of heater hose as a stethoscope to listen to each component individually. PLEASE BE CAREFUL OF MOVING PARTS!! Have a helper rev motor as you listen and as you turn a/c on & off

 

I'll give that try, thanks!