What is considered acceptable engine noise? My 88' 240DL B230F makes a rather audible ticking noise while idling that increases in volume as engine speed increases. The engine has reasonably low milage @135K and doesn't use oil except on long high speed highway trips. The noise is loudest during uphill acceleration at low to mid rpm's. At high rpm's the noise is not as apparent, is replaced by a low hum. What do you think? Exhaust manifold or valves? Is there anyway to test. There also is a clanking sound that comes every 2 or three seconds, hard to pinpoint, sound like it comes from the valve cover. Any ideas on this? If this isn't a problem what should I be looking for. Or should I just forget about the whole thing and keep driving?