the belt that controls the compressor is probably loose and if you can stand the noise then don't worry about fixing it. when it becomes more of a squeaking you can either:
a) wait until it breaks, at which point you won't have any a/c
b) not use the a/c and likely not hear the noise
c) fix it by tightening it, if it's an easy job then some garages will send someone out to the parking lot with a pry bar and ratchet and they will fix you up.