Took it to the dealership and they diagnosed my problem as a "compressor pulley" - whatever that is. Parts on order, should have by Thursday. I was so busy with work things that I wasn't really paying attention on the phone, but figured whatever their guess was I didn't care so long as it was under warranty coverage.

It was raining out and my truck was parked out in the rain so I didn't stand around asking for much of an explanation when I picked it up. When I call on Thursday to check on the parts status I'll be sure to find out what exactly they were talking about.

One thing about mine though - the whining sound doesn't come on immediately - it takes about 5 seconds at greater than 2k RPM before it starts, and then it's pretty noticeable from then on. The guy at the dealership concurred - it was definately 'something.'