Name:   Shortbus - Subject:   Serpentine Belt Date:   6/13/2016 9:32:22 AM

I had problems with such, it was the bearings in the idler pulley.  Remove belt, check wobble.

Wobble all pulleys and look at all from the side.

Ended up replacing the pulley and belt.  Good for 10 years so far on a 4.3 merc.