Pulley noise

I am trying to diagnose a noise in my motor. It seems to be coming from a pulley that engages/disengages another pulley (A/C pulley?), and only makes noise when DISengaged.

Can anyone tell me what this pulley is, and if it can be replaced? It sounds like it's either loose or has bad bearings. It sounds kind of like if you were to put a penny in an empty coffee can and rattle it around, and the noise goes away when the pulley engages.


thanks...

I think I have that or something similar to that on my 4.3L. A funny "chainy rattling" noise. Happens when coast around 30-40 and when accelerating slowly from around that speed... I have not checked to see if I could figure out what it is but it drives me nuts. Anyone know anything about it??