I'll let you know if I find anything out tomorrow. My car has had a similar problem for months, after the driveline is engaged the engine torque seems to go somewhere else than the wheels, and then everything smoothes out again.
It even happens if I'm already in gear (e.g. 1st) and suddenly hit the gas, instead of a wheel squeeking I get a thud, followed by the car moving. I've had a few mechanics say "seems alright to me".. yeah right. After shifting into 2nd at 6,300 rpm instead of the wheels chirping I get a jarring sensation, and then the car accelerates. Yeah that feels real natural, I've owned the car for two years what would I know. Really hard to explain but Ford should help me tomorrow. It seems just like motor mounts, could be.. we'll see.