I think something like what you describe might be going on with the one in my car.
I’m wondering if the “new” one I got has a bad bearing? You can see in Post #16, a video of me spinning the pulley, it seems to loud to me, but I don’t know if I’m just being picky.
Hand-spinning an alternator pulley does tend make a little noise, not from the bearings so much, as the brushes rubbing against the slip ring. Alternators require an electrical contact between the rotating part and the stationary part. Sometimes they’ll be virtually silent when spinning one direction, but they’ll make a noise in the other direction. My battery powered driver-drill does that too.
The brushes are new and not as smooth as they will be in a half hour of use. Maybe they will get quieter.