Well I ask a lot of questions and this one i did not have time to do research for so don't get mad. I replaced the serpentine belt on my LO3 and its making an awful rattling noise. I took the belt off and checked all the pulleys to see if there was any play. The tensioner pulley moves around is it suppose to have play? If i do need to replace it can i just do the pulley itself ($20) or will I have to buy the whole Tensioner assembly? Thanks for your help.

It should not have any play. If the play is in the pulley, replace the pulley. If it is in the tensioner, replace the whole thing.

Aye. The pulley should rotate freely but not be able to move in or out, up or down.

Yeah, tensioner shouldnt move, make sure its bolted all the way down, or replace it.