Humming sound apparent at low RPM's

[Parthery]

If it's coming from the rear of the vehicle, it's the rear end. Mine was toast at 48K miles.

Good news is it's covered by the powertrain warranty. Bad news is, at 52K miles, the noise is starting to come back. Not sure if its a design issue but I'm getting ready to take it back in.

 

[booyaltz]

Took it to the dealer.

Diagnosed and replaced water pump and tensioner that was damaged by water pump. They also said that it caused a small antifreeze leak.
They said the water pump was replaced under the powertrain warranty and the tensioner wasn't covered under the warranty, however "for the benefit of the customer (they) replaced the tensioner at no charge." I think they just said that the tensioner wasn't under warranty to make me think I got an awesome deal. Then they highly recommended a coolant flush, transmission fluid flush, brake flush, and fuel induction service, all for about $580.
I passed on the extra services and so they just replaced the water pump and tensioner under warranty.
Thanks for your help guys... the Tahoe is a LOT quieter now and more enjoyable to drive.