If the tensioner pulley is worn out it could be not "aligned right". Most of the time such a pulley will also make noise when the engine is running.
It is also possible that the tensioner has failed and has allowed the belt to move out of alinement.
Same conclusion: Replace the tensioner and maybe the pulley and maybe the belt too!
It is also possible that the tensioner has failed and has allowed the belt to move out of alinement.
Same conclusion: Replace the tensioner and maybe the pulley and maybe the belt too!