have a close look at your alternator pulley. It is a free wheel pulley and will wear out and wobble stick generaly wreck your auxillary drive belt and make all those rattle noises at start up and idle. When i had gone through my 3rd belt in 3 years I checked all the pullys with the plan of changing the tensioner again, but no its the alternator.. the alternator is £200,00 but the pulley and the tool to remove it with is only £70.00. got mine from local motor factors through hc CAR-GO parts suppliers dont believe the garage crap about needing new alternator just the pulley will do the job