Okay, any ideas are appreciated because it is driving me crazy.

2002 W208 M113, all service records since new, so well taken care of.

It began what sounded like a serpentine belt squeak when cold last summer. Since it is only driven in the summer, I kind of forgot about it until this summer. It only happens when the engine is cold, once warmed, no squeak. Mostly everything on the FRONT of the engine is brand NEW Mercedes parts.

Serpentine belt
Idler Pulley
Belt tensioner
Water pump
AC Compressor
Alternator
Viscous fan clutch
(also new motor mounts)

After all of these new parts... squeak is still there. The crank pulley looks straight and while the belt was off, I spun the power steering pump pulley (sounded fine), and "respun" all of the pulleys by hand. Once the belt was back on, and car running, I tried to locate the squeak with my stethoscope. NO LUCK. Interestingly... the sound seems to be coming from the passenger side of the engine somewhere.. If I start it with the serpentine belt off.. it seems like the noise is GONE.

Any ideas????

Thanks so much.