Cheers for everyone's input.

Been out in it today.
It generally drives and changes gear superbly!
But when your cruising at a certain speed and you just prod the accelerator a tiny bit you get a deep rumble coming from mid to rear of the car and the revs jump up and down by about 250rpm.
It doesn't happen when it's cold, only once it's warmed up.

There's also serious vibrations coming from the rear of the car over 70 which have only just started.