Vibration /noise at 70 mph

first time I have loaded up the freelander 55 plate TD4 and I got to 70 and there was a very loud humming noise that was cycling loud the quiet then loud , slowed down and it went away, almost, sped up the same it went away almost and a bit of vibration.
Since I have had it I have fitted a new clutch, flywheel, recon ird unit , new coupling bearings and renewed all the prop uj's did the torque test on the rear wheel to test the viscous coupling all seemed ok.
it made no difference if I have my foot down or just coasted the noise was still there until the road speed went down to 60 ish.
so the question, any ideas on what could be causing it.
The freelander does do this very slightly when unloaded but hardly noticeable at all.

Well just unloaded the landy and took it down the road, it now makes the noise when its empty at the same speed, will have to get underneath it and see if anything is giving way.

It sounds like something is unbalanced, what might be worth a try is to undo the front prop and turn it around one hole at a time and give it a run.

Had a similar issue after refurbing my VCU and had to turn the damper one hole. Not sure why but it made a mahoosive difference.