Squeaky belt(s)

I recently purchased a '99 VW Passat. I am getting a squeaking or chirping sound coming from a belt(s), I think. They all appear to be tight, so I am unsure as to what it could be. Does anyone have any ideas? I read something about a lithium stick? Any word on this?

Don’t lubricate belts, they’re supposed to grab and turn the pulleys. Several things possible here, 1) just try a new belt. 2) one of the pulleys is hanging up or turning stiff - with the belt off, test turn all the pulleys that you can. Sometimes it’s hard to tell about the power steering but all the rest should spin freely. 3) with the engine running, and the hood up, see if you can tell where the belt is sqeeling to help identify the culprit pulley.
You just got the car, used. Try the new belt first.

on a nine yr old car the serpentine belt tensioner is suspect.

there are several other possibilities too; bearing noise in the alternator, ac compressor, power steering pump, or water pump.

some more investigating is necessary to narrow it down.