Thanks Donnie! Tell me about the noise that the water pump makes. Mine is much more subdued as the car reaches full operating temperature (but is still apparant). This leads me to be highly suspicious of the water pump. It sounds like someone holding a plastic playing card in the spokes on a bicycle wheel that is spinning.
Also, how much is the water pump and thermostat? It is for the M119.960 1992 500SL engine. I'm thinking about doing the timing chain on this motor at some point in the near future. Perhaps this may be the time since all that MAY have to come off?