You need to check where the centre rear dogbone (or the dogbone end of the centre rear CVD) goes into the brake hub. If you notice wear in the slot of the brake hub, the dogbone can jam or cause other problems - including grinding noises, clutch slip (damage the clutch shoes) and damage the slipper prematurely.

This jamming can put stress on other drive-train components, as well as loosen grub screws.

Might be worth checking this before opening up the 2 speed gearbox. But basically, always trust your ears - if you can hear strange noises above the noise of a Nitro engine, you can bet something aint right.