All transmissions have free movement: if you rock and bike or car in the same way there is noise.
On a car there are normally "metalastik" joints that take up the free movement somewhere in the transmission, like this:
Rotaflex This is from a Triumph Herlad and the rotaflex coupling sits between the differential and the wheel, adsorbing lash between wheel and transmission.
On a bike the cush drive in the rear hub will do the same thing, but without anything that is designed to adsorb the lash between wheel and differential (bevel box)it is adsorbed by the belt and transmitted to the bevel box.
The M3W Centa drive has the same effect adsorbing load changes between engine and transmission, but it isn't enough. Something is needed between wheel and belt. A cush drive.
End of Rant.
