Car is a 1977 300D, 170,000 Miles. Great condition, well maintained, runs great.

I have started to hear a high pitched squeal coming from the engine compartment. It is very high pitched and has the nauseating sound of metal on metal.

It only appears at certain RPM ranges, (no tach). Generally I will hear it at 65 MPH with the engine under a full or at least a little load, i.e. if I lift of the accelerator it stops. Step on the accelerator it starts again.

Last nite, I checked it in the garage. Again, it only appears during certain RPM ranges. It is most audible at or below the firewall when I stick my head behind the air cleaner and as close to the exhaust manifold as I can get.

Help is greatly appreciated.

JCD