Could be a belt tensioner. Remove the belt (mark its direction with a piece of chalk or something similar before removing, and make sure you install it with the same orientation). Rotate each tensioner by hand and see if you feel any resistance or hear a grinding noise; if yes, it needs replacement, which is fairly easy. Also, of course, check the belt itself.
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2000 Boxster S, 6 speed, Sport Package, Litronics, LED tail lights, LNE IMS-B, OBC, Skybreaker wind deflector, Arctic Silver/Graphite Grey
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