Vibration from rear of TD4

Just over a year ago I had new prop carrier bearings and diff bushes, they lasted about 10 months so I had another set of bearings fitted and a poly centre bush fitted to the diff by a garage.
As soon as I drove away from the garage and hit 65mph I could feel a vibration from the rear of the car, like a badly balanced wheel (I’ve had them checked and all ok), I’m guessing whatever it is is what caused the bearings and bush to fail so quickly.
So, what can it be, it only does it between 60 & 70 and on the rare occasion it doesn’t do it at all.
I’m guessing the prop is out of balance and was thinking about using a jubilee clip to test this theory.
Anyone else had a similar problem?

Unlikely to be the prop out of balance.
First check is to make sure all the tyres are identical, with the least worn on the rear. Anything other than that can cause the VCU to start transferring torque, which then puts huge strain on the IRD, rear diff and propshaft, often manifesting as vibration in the driveline.

4 new tyres a year ago, recon Bell Engineering VCU.

Mr K said:

4 new tyres a year ago, recon Bell Engineering VCU.

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In that case, check everything carefully, especially things like the bolts securing the propshaft UJs to the VCU splines.

I took it to a FL specialist and he couldn't find anything obvious but there was some slight up and down play in the rear O/S drive shaft so he fitted a new one, so far so good.