It couldn't have been the balance pipe, since there isn't one. Checked the headlight bolts and found they were a tad loose (eigth turn maybe). Since I was down there, I gave everything a bit of a tightening. I did find that the headlight was aligned in such a way as to allow the bottom of the reflector to contact the two fairing bolts underneath the light. Seem that one of the above fixes alleviated the rattle. Thanks