I have a 98 E300 turbo diesel.

There was a chirping sound from the engine area. The engine has 199K on it and the belt has 96K on it (ie this is the 2nd belt).

I replaced the belt. The chirping sound was still there.

Last night, going home, when the air conditioner was on, a squeeling noise was coming from the engine. When I turned the air off, the sound went away.

This morning, I started the engine and left the air off. Whenever I reved the engine, the squeeling sound was there.

I would like to get some ideas on how to trouble shoot.

Thanks