Growling/Clunking Noise Coming from the Rear
A clunking or growling noise coming from the rear end COULD be a result of a breaking down of the gear oil causing a thinning of the viscosity of that oil.
When this happens the clutches can bind and a clunking, and growling can occur. This could be intermittent or happen all the time.
The Fix: The old oil is removed, the rear end cleaned out, fresh synthetic oil with an additive to reduce noise will be added. This should eliminate the noises.
This is a normal maintenance procedure and the oils should be changed out at certain intervals in accordance with scheduled maintenance recommendations.