It was indeed a loose wheel, got about an eighth of a turn on it.

glad you caught it in time! that was nice and cheap then.

Similar incendent at cadwell the other week, fortunatly an eagled eyed skidlids spotted the problem, not only were the sprocket carrier nuts within an MM of falling off but the wheel nut was not torqued up as it should have been :(

I seem to remember that you get a very similar clonk if the rear wheel locating pegs break too - dont ask me how I know, but I still have a spare one, 5 years after selling the 916 ;)