Knocking/ steering wobble

hi all , I’m after a little help I have a RR vogue HSE on a 08 plate, just got it, when driving slow or below 50 it’s great but go over 50 and back off I get a knocking and a wobble on the steering wheel, it’s like when under load it’s fine then when the front becomes light it happens.
i have checked the last mot and it got advised on offside front suspension arm ball joint, could this be the problem or any ideas..
Cheers

Yes.
You’d notice it more when turning one way or other,
I’d check UJs on front shaft in particular. The play is not always easy to determine, you will feel it more than see it. Would be cheap fix too

Wheel balancing?

Ball joints can cause vibration at speed.
If you do any ball joint replacement, do them in pairs.

+1
You have 2 options -
investigate yourself at much cursing and tutting, or get an indie to lift it up on the ramps correctly and find out within ten minutes exactly what it is

Check the prop shaft mine was vibrating and found previous owner had removed prop and not lined it up properly when put back on