Shaking steering wheel help..

[Carrerax]

Ok, so my wife calls me at work today saying that the X5 (2001 4.4L 80k miles) started shaking really bad (in the steering wheel) and feels like the wheel is going to come off (RF). After she stops and parks it in the garage is is making clicking noises (car off, parked) and she can smell something like a plastic or something hot. She said that it only does this when the car has been driven maybe 10 miles or so. I got home from work and it sounds and drives perfectly. I did a search and didnt find anything. Any ideas? I don think it is an axle since it isnt consistant. PS pump maybe or steering rack? Help!!! Thanks in advance! Mark