Originally submitted by T:
===Knocking from one or both sides of the rear axle:===Knocking from one or both sides of the rear axle with the throttle shut and the vehicle coasting.
===Cause:===The sidegear bearing for that axle in the Differential Carrier (the Hemisphere)
is worn into an oval shape. The differential end of that axle is being stirred around in a circle and the axle is being flexed with each rotation. This can cause an axle to break.