Based on your symptoms, it is probably your 5 year old belt, because it does it at start up, and not all the time. If it did it all the time, it is probably the tensioner or an associated pulley. There is probably moisture on your belt. The tensioner and the belt are notorious for going bad prematurely.
Instead of getting a the same belt from the dealer, go to Autozone or the like, and get the gatorback belt, and you can put it on yourself if you are mechanically inclined. If not, take it to your mechanic, and insist he uses the gatorback.