Alternator noise?

From : napalm heart

Q: a squealing noise was being made. i did the belt off check - no noise. i spun the pulley back and forth on the alternator it made some rough noises then nothing. i put the belt back on - no noise. my guess is that the brushes werent in the proper place and by moving things around i caused them to go in place. is there a service interval on the alternator my truck is a 97 dakota with 175000 miles on the original alternator. no problems with the alternators operation. comments thanks ken .