Deffo a bit suspect, but I would remove belt and check smoothness of all pulleys in system and then run engine ( for short time only as no water pump or alt will be operational) with the belt removed, this will indicate if the noise is indeed in the aux belt system or not.
so, you say ac seized. So do you now have replacement good ac compressor? If yes then when old compressor failed it may have put a lot of force through the tensioner and damaged it to how it is now ( if it is tensioner)