Not on my car, but Joel'* new Regal started making this noise on Friday, So today I removed one belt at a time.
Removed the supercharger belt, noise was still there, removed the accessory belt, noise was gone compleatly. I changed 1 litre of power steering fluid just for kicks, that didnt help. All of the pulleys feel great, no grind, no back and fourth play. The AC compressor when the car is off is obviously not engaged, so I couldnt tell.
Car running, normally with the AC off, the noise gets louder, AC on it seems not to growl as bad, except for this time, it growled alot.
So, Gearheads, what do you think?

Sounds like a bearing to me. :?

I had a bearing on a pulley go bad on mine that made a similar noise. Spinning and checking with the belt off, you wouldn't have known there was a problem. Try spraying some WD40 on each of the pulley bearings to see if one of them quiets down.

I had the same type noise for a few weeks before my compressor pulley seized.