When I stop at the lights for a while and throw the bike into neutral, I notice that the revs slowly start to decrease and the bike vibrates a lot more - if I pull the clutch in it doesn't happen. I've also noticed that if I start the bike on the centrestand in neutral, the back wheel will very slowly start to move around. Does this mean that the neutral gear is slipping in a similar way to how a clutch would? Is that even possible? And what can be done about it?