Just been looking at a Cooper S that at making a tapping noise from the drivers side of the engine (quite loud) but intermitant. I think it could be something to do with the tensioner I can see the top of it vibrating I think with the noise??
But I have also noticed another thing - The car has had modified pulleys (inc the tensioner pulley) It looks like the tensioner pulley is rubbing on the bracket as the side face of the pulley is VERY shiny.
Trouble is the owner of the car is due to drive down South Sunday to start a new job