Defender 90 td5 2004 "pop" "plop" noise from rear axle

Hi all I've been trying to diagnose a popping noise on my 90 for a while now, and I seem to have found a situation that makes it so it more frequently.

It doesn't do it all the time but I have noticed it tends to do it say if I reverse back fairly quick then stop then set off in forward gear. Just as I start to get moving forward again something from the rear end goes clonk or pop.

It's almost like the change of forward and reverse motion makes something jump or knock. The noise kind of sounds like when you put your tongue to the roof of your mouth and make that noise.

It's had new half shafts and drive flanges new shock absorbers and springs and all bushes seem good.

Radius arm mounting rubbers to chassis have a bit of a gap behind them and this opens up a bit more if you jack the body up but let the axle hang down .

Any ideas?

It's 2004 done 60,000 miles might of done a bit of towing before me I'm not sure

sounds like slack in drivetrain, a lot clunk to an extent if you drive em like cars

but check your aframe balljoint and your prop ujs.

Uj's all seem good and I can't seem to make the a frame joint move it seems solid?

I was wondering whether it could be something in the hand brake mechanism? Getting stuck perhaps and then flicking itself back on the change of direction.