I dont know how severe his is, but my X5 does something like this too but just a little, and depends on how you apply the brake, as we know our brakes are really touchy at first, well if i tap mine to that beginning grabbing point, the steering wheel you can feel and see it does a slight jolt usually to the right, now if you progessivly apply it, it doesnt.

Basically i think at least for me its just the grabby brakes or road imperfections, slight waves and such usually by stoplights.

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2006 X5 4.8is Fully Loaded