The fan belt rides on the water pump, on the harmonic balancer, and on the generator?
They are all attached to the block (and move with the block).
I'd guess a bad bearing in the water pump or in the generator (and, more unlikely, a loose/wobbly harmonic balancer).
Also, you might as well check the sizes of the grooves in all pulleys - are they the same - what width fan belt do you have?
