Odd noise at warm idle
 

When my '81 W123 240D is warmed up and idling there is a intermittent clicking or chirping noise. It's coming from the area near the alternator so I thought that was the problem but I replaced the alternator and I still have the noise. It only happens when the car is well warmed up ,not when it is first started. If I squirt water directly on the belt between the water pump and the alternator the noise stops but comes back as the belt dries off. I replaced the water pump not too long ago. That's the only other thing on that belt. The belt also looks good. Any theories?

Throw a cooling fan at it too.

I would replace the belt, a relatively cheap fix, may have very small cracks which will cause such noises.

The crankshaft pulley is unlikely to make a chirp sound but that is a disaster if it comes loose as they do on occasion.This is the pulley that drives the belt and is the first thing to check. If it is not loose keep looking. the belt will have to be detensioned to check it. Grab the stethoscope and start listening.