I have had most things go tits up at some point, might just be the tensioner. Get a socket on centre bolt and see if it moves freely, or take it off its only a couple of bolts put it in a vice, it should be tight but smooth. ( no sexual innuendo intended). could be one of the pulleys if so the bearings are dirt cheap no need to replace the whole thing, if its the damped crank shaft pulley that makes a hell of a racket. Best thing is take the aux belt off and have a listen and see if they all spin freely. should be no play in crank shaft pulley get a lever on it and give it a tug.