X type 2.2d Estate sport. I have vibration only under power ( not when coasting) at around 50mph and above. It is quite severe. Shaking steering wheel. I had wheels balanced today. Still there. I also noticed a noisy clunk when I change gear especially when I put it into reverse and start reversing. It happens going forward too after each gear shift. From what I have read ( I am no mechanic) it might be a universal joint that is causing both things? Any advice??? Also I understand on this car you cannot replace the u joint as the drive shaft comes as a sealed unit. Is this true? The transmission noise is a loud clicking, minor clunking. Many many thanks. Patrick

 

Vibration when under load is usually due to inner cv joints. You are correct that they cannot be repaired. Replacement is the only answer.
The clonking at gear changing could be the central engine mounting. This happened to me a few years ago.

Roger