My '91 240 was running quietly. Then the drive belts came off b/c the alternator pulley was out of alignment b/c the bolt holding it in place was missing. The engine overheat light came on, but I only drove a short distance, maybe 2-3 miles. Belts were replaced, and then about 2 days later I noticed a rattling noise that was not there before. At first I only noticed it when I stepped on the gas pedal an the car was accelerating. Now, I think I can hear it when I start the car, it dies down a little after a while, but still always gets loud when I step on the gas. At first I thought it was an exhaust leak, but there isn't one, and the noise is definitely coming from the engine compartment. I just don't know if it is inside the engine, or something else. I had the oil changed, with three quarts of synthetic and 1 quart of LUCAS Oil and it still makes the noise. What is it? It is driving me crazy. The engine has 83,xxx original miles. It almost sounds like a diesel engine, but again, rattles even louder when accelerating.