If it bounces a lot at idle (mine barely twitches) you likely have a fair amount of red "dust" on the alternator pulley cap. In any case it's probable that your alternator clutch is shot, not uncommon, and that's your squeak. The clutch itself can be replaced (IDparts has it and also has the whole alternator at a reasonable price) although I understand, never done it myself, removal of the clutch is a bit of a problem. Alternatively some have been able to source a lifetime warranty alternator from like Autozone pretty cheap (ca. $150 IIRC) or
http://www.maniacelectricmotors.com/ rebuilds them or used to.
FYI don't go cheap on the clutch at some local shop, although they might could do the removal/install if you bring in the alternator and new clutch, as the cheaper "reactive" clutches won't hold up and a solid pulley replacement will do nasty things to other components associated with the serp belt.