I have a 2001 Duramax with 167000 miles. There is a contiuous squeaking noise coming from the front of the motor. It started with a chirp ever second or so but now it is a constant noise. I tried replacing the belt and the tensioner and the noise stopped for a week or two. I tried spinning all of the pulleys but no of them seemed loose or made noises.
Also, the motor just started making knocking noises at about 65 MPH or about 2000 RPMs. This happens wen I am travelling down the road and give it gas or go up a hill. It does not make the noise at lower RPMs.