Buy a mechanic's stethoscope to help identify what pulley is making noise if you are not planning on replacing all of them at once. They are super cheap and very useful.
Belts are very easy to do, and should only take like 10 mins. I have a spare of each belt if you want a good deal on them, I could hook you up. The main serpentine belt is Continental and the smaller AC belt is Genuine BMW. PM if you need, if not I'll keep em on my shelf for later down the road.
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