Check the idler pulleys on the drive belts. Take the drive belts off and spin the pulleys by hand. If they click or feel rough when truned, they have gone bad and that is the source of the sound. The bearings go bad inside the pulley. They cost about 13 bucks on the east coast from NAPA. The original part number off the bearing is NSK 6203DUL1. Drive the old ones out with a hammer, socket, and some blocks of wood. I suggest using a C-clamp to put them back in since it is easiest on the bearings and has the lowest chance of damage. I also suggest using the old bearing up against the new bearing and a piece of wood when putting new bearings back.
Last bit, try to get the bearings with the rubber seals on the races and be careful not to damage the new races or else you will be doing the job all over.
If the pulleys are not the problem, it could be the bearings in the A/C or the alternator. Check these by using a long screw driver pressed up against the ends of the parts while the motor is running. Placing the andle against your ear will let you hear the sounds made by the bearings. Any clicking indicates a bad bearing.