So I keep getting this intermittent squealing/squeaking noise from the belt. I was finally able to track it down to the tensioner pulley, but the noise is coming, not from the bearing, but from the belt occasionally riding over and rubbing up against the edge of the bracket. It doesn't always do this, but seems to be doing it more often than it used to. Is there something I can adjust to get that belt to ride in the center of the tensioner pulley?

 

just buy new. the shaft that the bearing rides on is probably excessivly worn. when its tite there will feel like there is no play. but with the belt off, you mite notice the pulley is able to move around a bit, but the belt cant go sideways.

 

When this happens it's usually because the pivot point that the arm rides on is worn, not just the pulley.
Replace the entire unit.