Might be a broken spoke in the wheel, or a loose tail light assembly. I think they have a history of working loose and breaking of into the back wheel with a lot of off road riding. Have a look to make sure all the tubes on the bottom of tha air box are attached where they should be. The clear drain off has come away before on mine.
The swing arm is hollow maybe a stone has found its way in there?
Just a few suggestions to keep you busy Dual. Good luck.