this weekend my mates s2 turbo has developed a problem. its making a a tapping noise coming from the top end. its quiet on tickover but when you start driving you start to here it. its also lost power aswell and dosent seem to want to pull over 3500 revs. the turbo spools up but it just dosent go anywhere. this has happened since the knocking/tapping has a happened any advise would be appreciated. thanks