Look for a cross member under the car.
Locate front drive shaft (between front axle and transfer case)

2008 BMW X Series (E53,E70,E71,E83) X5 4.8i 4-WHEEL drive SHAFT/INSERT nut

In the image above, part #2 is where the problem is on the "U" join section.
Check for play, it is accessible without lifting the car, if you are thin enough.

Good luck.