I had the pump bearings seize up and COMPELTELY fail on me, stranding me in raleigh (100 miles from home and with my girlfriend [who's now my ex
]) for 5 days until I could find a shop to help me fix it.
Once they fixed it, a week afterwards the fan they put on it lost some blades. What I figured out was that the vanos solenoid is *suprisingly close* to the blades. If there's any play in the water pump shaft in any direction other than perfect rotation, replace the pump asap and be sure it's got the metal impeller. (replace thermostat & change to a metal thermostat housing while the cooling system is drained... while your at it... cheep & preventive) You might want to see if you could put some washers as spacers between the fan and the fan clutch to give it a little more distance from the vanos solenoid, if thats what you think it's hitting.
You can get cheep (& OEM!!!) fanblades at autohausaz.com. The one I got from them hasn't given me any trouble at all and is very balenced.