Took my cup in to the dealer on saturday so sort out the resonance that I get at 4k rpm. It has already been in once. I actually got chatting to one of the mechanics who did actually know what he was talking about. Apparently the rattle can be caused by either of two faults:
1) the wiring to the lamda sensor (he actually said oxygen sensor) becomes loose and rattles against the heat shroud above the exhaust pipe
2) There is a fault with some of the center exhaust sections which have to be replaced
He actually got my car on the ramp there and then and fixed the problem, took 5 mins.
Hope this may help cos it can be anoying as hell
