Stupid question, but are the rims stock? There's always talk of offset/staggered rim setups causing issues on Xi models.
I think the previous posters talking about CV failure are talking about torn boot, grease spilled out type failures. Axles with grease in them tend to stay happy.
The only other idea i can throw out is that the transfer case, diffs and transmission are all listed by BMW as a lifetime fill fluid. I changed all of these finding the fluid in varying condition. The transfer case was by far the worst.
My thought is really broken down fluid in the t-case could cause some drag, and the hopping/scrubbing. I may be completely wrong here, but the t-case fluid NEEDS to be changed at some point.