Very good info. Mine has done this on and off for a year. Looks like it may be slipping too and I can see where there's metal transfer on to the belt from one of the pulleys.

I had to replace my tensioner and idler pullies this year....they began to drag and it was causing me to toss belts over and over every 50 miles or so. After over $100 in belts in a month...I decided to change them (the pullies instead of just the belt) and it worked. They may seem to spin ok....but they had a drag under higher RPMs.