when you take the belt off spin all the pulleys by hand and see if any of them don't feel right. Or with the belt on take a mechanics stethoscope and touch the cases of the components. Like the alternator case and PS pump if you can get to it. Disclaimer though, careful the engine has to be running to do it this way, so there will be belts spinning. and don't hit any moving parts with the stethoscope, your ears will thank u.