1983 300cd recently developed a clattering noise seeming to come from near the front of the engine. This is different from the normal clattering that diesels make and is somewhat intermittent. Thinking it might be the water pump, I changed it our for a new Bosch unit, but there was nothing wrong with the old one. I'm afraid to drive it in case the noise is a timing chain problem. Any ideas other than replacing the timing chain. Something maybe wrong with the tensioner. Engine has good oil pressure.