rumble when let off accelerator

As title says I got a loud rumble! If I'm going anything above say 45 and then let of the accelerator I get a massive rumbling noise! Put power back on even just a small bit it goes. So bit of play in the drive system somewhere I'd say. Anyone else had this and is my gearbox on its way out?

Its been like it a while now but I'm in 2 minds if shall take it off the road as my workshops jus being built so I could give it a mini rebuild.

Diff on the way out?

Try removing one prop, putting in diff lock and driving to see if that makes a difference

If not repeat with other prop off

Process of elimination!

First port of call is always props universal joints or prop sliding joints, even slightly worn sliders can cause bucket loads of noise.