XC60 shudder 45mph rear diff?
 

Hi and a happy new year to all.
I have just bought an auto XC60 2.4 d5 2008 with 134k miles.
Yes I am dumb.
Anyway all is good except for a sudden briefish shudder from the rear of the car at 45mph when accelerating quickly. I couldn’t test drive it properly in the centre of Nottingham!
When normally driving there is no shudder.
It doesn’t appear very whiney, but it is the first XC60 I have had.
Have I made a big mistake?
Having agonised over cars before searching for the ideal motor only to be be blessed with unheard of faults I figured just toss a coin and buy “something”
I’ve searched but has anyone head this issue and if so any idea of the solution?
Thanks

Could by anything from wheel bearings to driveshaft universal joins to worn torque converter

Keep narrowing down the exact way to reproduce the issue then see a mechanic and take him for a test drive.

Thanks.
This is my plan. It’s going in on Friday for a full service and belt changes I am just trying to get a feel for what might be wrong. I’ve replicated it a dozen times and I happens just after a third gear change when accelerating hard. Going to take it up some steep hills and see if it happens sooner but on the flat it is always at 45mph.