Hi Abiella,
It happens when the couplings come loose or arent tightened enough. Its a common mistake made by not wanting to tighten the couplings for fear of threading the alloy.

I used a removable loctite when I put mine back together and it seems to be fine 3000klms later.
Fixing it is pretty straight forward just be mindful of the shims that fit on the axle. Make sure they are facing the right way and the right side. When I dismantled the gearbox, I took care not to pull the axles out until the entire diff assy was apart
