Engine belt noise - HELP

[nc318]

I've got a '98 318ti with what sounds like belt noise. It's a high pitched noise which seems to almost cycle with the engine. I've gone back and forth with the dealership replacing belts, water pumps, pulleys... etc. They've even tried greasing the pulley. One mechanic even said that it was inherent to the 318's and that he couldn't figure it out.

Others tell me that when they disassemble the system, clean the belt, and make an inspection that they don't hear anything, and by the time I get it home I can hear it again.
Belt dressing seems to help in the short term, but I don't have time to keep messing with it. Any ideas?

[Panzer_M]

Most of the noise on the m42(95s) is the intake/airbox.

but most BMW 4cyl are high strung sounding.

[nc318]

Thanks for the info Panzer M. Is this also the reason why the noise can only be heard during idle and not while revved or while driving?

[Adog2107]

check ALL of the pulleys....def. sounds like a pulley problem...