Sounds like fairly normal drive train slack. There is a little more "ping" from some metal resonating. I would look into typical wear parts like the guibo and the CV half axles as well as the rear bushings. My first thought is maybe the front driveshaft is vibrating when the slack comes out. Think of it like water hammer in a pipe: when you switch from forward to reverse the transmission output shaft might turn a quarter turn before all the slack is out of the system so It hammers pretty good.

__________________
2011 E70 • N55 (me)
2012 E70 • N63 (wife)