A friend of mine has a C series Kompressor 1994 (not sure of the model).
He has noise from the front of the engine that sounds like a metal on metal rattling with a slipping belt. After look at it for him, I thought it was coming from the fan clutch. I assume this model has a clutch because when the engine is off, the fan spins freely. My guess is that the clutch is not engaging fully and is causing the "slipping" type noise.

Is this a common failure? Does this sound like a realistic possibility? From my research it seems that is actuated by a solid state device and not a centripical type device. I know he had the water pump replaced a year ago.

Lastly, if this a fan with a clutch, why would MB do that? What a F'd up, over engineered way to do things. An electric or direct drive fan has been proven for years....

__________________
1982 300SD
1967 250S
...what was I thinking......