I had the same symptoms; noise and loose fan blade. I wiggled the fan blade and noticed that the fan-clutch and belt pulley wiggled with it, I knew it was the water pump where the bearings on the shaft were loose. Unless it was apart recently, it's unlikely that the bolts holding the fan blades onto the fan-clutch become loose, or that the fan-clutch unit un-screwed itself from the water pump main shaft. Very likely the water pump and again to tell, wiggle the fan blade and if the fan-clutch and the belt pulley assembly will move with it then that will tell. Although my car is a 98' C280, the engine is very similar (V6) and they share the same water pump.

If it turns out to be the water pump, you can replace it yourself for under $150. (the dealer quoted me $750ish!). I bought the water pump, gasket and thermostat here on shopforum.