Originally Posted by planenut

I still doubt it is the drive belt jumping teeth, it just won't happen. I could go with
1 Calum's swing arm bearing adjustment,
2 belt slap or (more likely) the
3 nodding BB with the NVH. Have a check around the BB and see if there are any signs of fouling?


or
4 maybe the tyre losing grip suddenly reversing the tension on the belt?

M3W5sp 2015, MSCC, MTWC, Oxon UK