2000 E39 528i 6cyl- My main belt broke today (pump/alt/crank), so I installed a new one. Not too hard. Started the car and after about 10s had to turn it off. I noticed the radiator fan/pulley assembly basically rocking /tipping front to back and clunking as it did. What I could really see is the big fan clutch lock nut moving fore/aft and I assume the water pump bearings were too, but I could not see to confirm. It did not do this before I changed the belt. I can't imagine that I did anything to precipitate this by changing the belt. The only thing I touched was the 16mm nut on the tensioner. maybe the tighter belt is pulling more on the water pump? Doesn't make sense since the tensioner should keep constant tension. Any ideas as to why all of a sudden this is happening? Water pump bearings, fan clutch, loose pulley attachment? Coincidence? I'm stumped.