BMW Repair: Chirping, uncommon problem, chirp

Question
Hi Paul,
I own a 98 318i that has developed a chirp.
I replaced both belts and the altenator/water pump tensioner. The chirping starts after about 10 minutes of driving (usually during deceleration). I'm guessing it's one of the pulley bearings but not sure which one or how to pin point the problem. Any suggestions?

Answer
you are obviouslt mechanically inclined. 1st remove the a/c belt and run the engine. is the noise gone? if so, the pulley/tensioner on the a/c belt is probably bad. not an uncommon problem. if it is still there, remove the main belt and run the engine briefly. if the noise goes away now and you already replaced the tensioner, then yhe idler pulley is probably bad. also, with the belt off, spin the accessories, waterpump, alternator, etc and listen for unusual noises.