Odd Engine Noise - 1995 C220

[ctaylor738]

Our 1995 C220 has about 75K miles on it, and has always been reliable and trouble-free. It was a Starmark car when we got it in late 1999 with 39K and has always had maintenance by the book by good indies.

It has always had a noise that puzzled everyone and seems to be getting worse and more consistent with time.

I would describe it as a constant rattle from the front of the engine. Does not change with RPM and independent of engine or air temperature.

Yesterday I got out my most sophisticated diagnostic tool - a 3' length of heater hose - and listened around the front of the engine. The best fix I could get was the thermostat housing and the large horizontal metal tube leading to it that holds the various sensors. Removing the front snap-on cover changed the resonation of the noise.

It does not seem to be coming from the fan, water pump, valve train or crankcase. The thermostat and engine temperature appear to function normally - warms up and sits just above 80 degrees on the guage - and never any overheating problems.

Ideas welcome.