Water Pump Noise?? Please help!!

[stummala]

Hello folks,

I've got a problem that's been nagging me for a few months. When I start my car cold, I hear a whirrring rattle from the engine (M119.960 V8 from 1992 500SL). As the car heats up after driving for 15-20 minutes, the noise is more subdued but it is definately still there. This is very consistent and happens everyday.

Finally, yesterday, I removed the serpentine belt from the engine and then started the car. The noise was COMPLETELY gone. :-) I was feeling pretty good knowing that it DEFINATELY is a drivebelt driven accessory but which one??!? I tried listening with a stethoscope to no avail. I tried turning all the pulleys with the belt removed but they all seemed fine. Now add this to the pot, in the last 6 months (and roughly 14,000 miles ago), I've replaced:

power steering pump
alternator
smog pump
a/c compressor
belt tensioner

Therefore, that leaves....the water pump.

Now, when I put the belt back on the car and retension it. I can feel an EVER SO SLIGHT, and I mean to stress the word SLIGHT play in the water pump pulley. My question is this:

My water pump currently doesn't leak, the engine temperatures remain steady, however, it has never been replaced on the car. Also, the fact that the noise gets less when the engine heats up seems more consistent with the water pump (hotter coolant expands tolerances, etc.). Can a bad bearing throw off the position of the plastic impeller perhaps causing the noise? Once again, it sounds kinda like if you spun a wheel on a bicycle and inserted a playing card into the spokes.

I'm tempted to pull the pump and replace it with a new MB one.

Also, I've checked all fluid levels (power steering, hydraulic fluid, etc.)

Thanks and sorry for the long message!

Satish
1989 560SEC - with M119.960 V8 32-valve transplant
1999 E430 Sport