Fan Clutch Grinding-Rattle
My 2006 330ci with 25000 miles developed a grinding-rattle noise at the front of the engine. I first thought it was the water pump. Holding a steel rod against the water pump and my ear with the engine running proved it was not making the noise. I checked the air conditioner compressor and the idler pulleys were not the noise source either. Then I noticed the fan was wobbling slightly as it turned. I found the fan could be moved back and forth about 1/4 to 3/8 inches. The bearings in the fan clutch were bad, causing the fan to cavitate making the noise. Using a 36mm wrench and clutch holder (Left hand thread) I removed the fan with the plastic shroud. The clutch nut wobbled in its socket. After replacing the clutch with a new part the noise has gone away. Check this out before replacing the water pump if it is just a noise. If you find leaking coolant from the pump then it is time to replace the pump.