alternator belt .
tension check by touch, if there is some give, its need tightening,
just had my 100,000k service done, pump and all belts, and plus there new, let them wear in, but also get them tightened. not to tight though, if you put to much strain on the alternator and can wear out the bearing at the back of the alternator i think, its connected to the pulley that spins it.
hope that helps, i get about 3seconds of screeching now, not 1min like before