I have had my truck for two weeks now and the weather just broke so I have been driving with the windows down instead of using the A/C. As I pass by cars, I can hear a chirpling sound. If this were a gas engine, I would say the fan belt is squeeking because it is too tight. This is my first diesel so i am not sure if this is normal or not.

94 F250 7.3 IDI turbo

 

I get that a lot in the area of the tensioner, or possibly the idler. It comes and goes on mine, so it is hard to narrow.

 

mine did this.
the tensioner was shot,so i knew to replace that.the loud chirp was still there,so i put a new belt on.that took care of it.even though the belt looked perfectly fine.

 

ill go with the tensioner as well. i put a new belt on and it started making that noise. i kinda like it.

 

If the noise is engine speed related, idler pulley or vacuum pump would be the first things I would look at.

If it is vehicle speed related, U joints, brake pad squeeler.
Could be a couple other things depending on the transmission and cab style.