Have a 91 Camry with a rebuilt engine (less than 20,000 miles). Occassionally, the car makes a rattling noise- when the A/C is on. Once warmed up, noise goes away. Or i can turn the a/c off, and it stops.

Bad belt? Bad compressor?

 

I noticed that the rattling sound stays constant- no increase in speed when the engine is revved. So I checked my two electric fans and sure enough, one seems to have bad bearings or something, as the fan balde rattles and can be moved quite a bit.