if you read some of the literature on the E70 xdrive, you will find out that the all wheel drive system is a "proactive" system that calculates traction and accelerator movement to best apply the tourque and power before the car starts to move- Flexray can make it happen in 0.1 seconds (100 ms). If you find that when you depress the gas pedal suddenly and the car hesitates for about 0.1 sec, you know its the xdrive working properly for you so you don't get the mad back end sliding.
If the hesitation is longer than that, i'd an engine issue.
When I first started to drive my 4.8i it did experience the hesitation. I'd press on gas, wouldn't move, so i'd give it more, then just BOOM! shoots forward, then I panic and pull my foot off the pedal, and the car jerks and everything inside it ... then other people wonder if I've gone mad
