Hi Rodge, I'm no expert in this sort of thing but my mate had exactly the same problem with his 52 Mk4 Golf GTI. After having the wheels balanced and everything he was told that he needed his steering rack replaced (the arms could have been close to actually snapping away therefore he would lose all control over streering which is pretty dangerous). However, once this was sorted the problem still occured. He went to another garage and they told him his driveshaft needed replacing - as you mentioned (which is really expensive by the way). Once it had been replaced the problem finally went away. Someone could probably give you some better advice with this but I hope that helps. I wouldn't recommend driving the car unless absolutely necessary in case it is the steering rack, and it wouldn't be good if you were driving down the motorway at 70mph and the arms snapped. Good luck :D