I've got a knocking noise in the "bottom end" of the motor somewhere. My mechanic couldn't zero in on it without pulling the engine apart. Mine is really loud @ 1500 - 2000 rpm's.....then un-noticeable @ higher gears and speeds. Mine's a 2000 with 140k miles on it. According to the mechanic, I have a lot of sludge build-up in the motor. I'm just living with it until it eats itself or I can afford to trade it in, as it is not worth having an engine re-build or swapping motors. The truck's only worth about 3 grand......no telling what a re-build or motor swap would cost.