cyclic vibration

Evening all.
I have a cyclic/pulsing noise/vibration coming from the rear of my disco. It comes in at around 57mph and goes after about 70mph ( sometimes). Its worst at full throttle acceleration and goes away if you lift off. Similarly if you take it up to 70mph and let it slow down or dip the clutch it disappears and is not there whilst slowing down. First inspections shows everything to look ok with no joint play.
The rear tyre are both nexen road tyres whereas the fronts are scorpion at's. I'm not sure this is the problem though but do intend to swap fronts for rears in an effort to try and solve the issue ( when its drier and warmer). Other than that I'm stumped. Its like a panel resonance but loader and more defined.
Any ideas??
Thanks.

Have you checked the rear prop doughnut & spigot bush ?
I've just changed ours for exactly those symptoms & cured the vibration.
The doughnut didn't look too bad until you flexed it.

Paul

2001 D2 TD5, 184,000 miles & climbing

I've only visually inspected the doughnut to be honest. I cant get it in my garage due to height and my drive is steep so cannot drop the prop as it'll roll downhill. Will try at the weekend to get it dropped and see. I should have added that i also have a clunk when going off and on throttle coming from the same area. Did you have that also??
Thanks

There was a clunk - now reduced, but not eliminated.
Part of the clunk could have been the much increased flexibility of the knackered doughnut, but what's left is probably the slop in the transmission ( transfer box & diffs)

Paul

On and off throttle clunk......check out the rear suspension "A" frame ball joint connecting top of rear diff housing to chassis.