Check for proper alignment of pulleys. I had a similar problem shredding vbelts for my AC. It was cocked and would would make the belt rub on the front flange of the pulley. You couldn't see the angle of it head on or from above, had to look from just the right angle from the side. Get a ruler or some kind of straight edge and try to put it across the front of the pulley, this will make any misalignment more obvious.
Maybe your P/S, A/C, Alt, Tensioner, etc. going bad and cause some drag, which would then cause friction and heat then cause the belt to start to fail.