Just a thought, might work though. If you got one of those lasering levels that projects a line could you use that across the front of all the pulleys to find the culprit. I could bet there is a pulley on backwards or with a extra washer/spacer behind it. If you cant find one that is physically damaged that is.

I am no mechanic but I did stay at a holiday inn after my wife kicked me out for spending all my time and money on my truck