As Jerry suggested, change the belt. Pull the old one and take it to your auto parts house and they should be able to measure and replace it. I would get two belts, one the same size and one the next smaller size. Your present belt is probably stretched and worn and the same size is probably the correct one. If you are lucky, the part number may still be visible on the belt.
I have to replace the alternator anyway so replacing the belt is no problem.thanks.
