my car is having a sharp knock in the gear box

[scoobydoo]

i had taken my defender to the desert last week and i heard a sharp short knock when i was accelerating or decelerating on the desert the noise was coming from the area of the gearbox i could not only hear it i could also feel it. can anybody advise me on what could cause this. thanx

[Macrover]

Check for gear oil leaking signs under the gearbox oil sump, its gasket is tend to leak after certain age.

or top up gear oil and see if it still knocks.

Sounds like gearbox running dry