It's not the water pump. The only connection b/t the pump & the fan on the M103 is that they're driven by the same belt. I just finished replacing the "bearing bracket" as it's called in the parts listings. It's a casting that bolts to the front of the engine & holds the bearing that the fan & clutch bolt to. That bearing is a fairly good sized double row ball bearing. Mine wobbled around & made growling noises for an amazingly long time before I discovered the problem.

Look down between the fan & engine, with a flashlight if needed. Grab the tip of a fan blade or two & try to move it front & back. If it rocks on the clutch, bad clutch. If the clutch rocks with it, bad bearing, need the bracket assy. They typically go for $85 on eBay. That's where I got one. It is a Lemforder brand, an OEM for MB. In my case, the growling noise was the bottom, back edge of the fan pulley (no grooves, flat side of the belt) rubbing on the block. It didn't wear the pulley out and just shined up the block, so no real damage & it got reused.

I'm not going to go through the whole procedure, as it's detailed pretty well in a number of threads. I will say that it's much easier if you pull the radiator first. Mucho more knuckle clearance. while you're in there, might as well take a look at the other idler bearings and the tensioner, too. And, of course, the belt.

HTH,

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Norm in NJ
Next oil change at 230,000miles