There could be a problem with the diff or the driveshaft as the bike has not been ridden much. If the seal on the drive shaft where it connects to the diff is damaged then moisture can enter and if there is a lack of lubrication on metal surfaces on the diff or the tail shaft spline they can rust and then cause a vibration under load at low speed. This can result in the replacement of the diff. I could be an expensive fix.
Bluey replied on Dec 11, 2016