Had the old belt on the car from 2006 until 3 weeks ago. Never had any problems until then. It would squeal a little when I would start the car, but that was it, and then I noticed that there was a groove in the under side of the belt that matched perfectly with the tensioner. After three weeks my new belt has the same squeal on start up, and the same groove worn into it. I'm posting a picture of a factory tensioner so you can see the type of groove it's wearing into the belt. My question is what would cause this? I'll try to post a picture of the belt after work tomorrow. I know the belt size is correct because it worked fine for 7 years.