i was just thinking do u get like a huge boom in the gear box when it takes off or changing from 1st to 2nd mainly this is if your a bit rough on the pedal?
to explain better it sounds like some piece of metal jumped and fell into place roughly

the sound is like a rough knock but its clear its from the gearbox, my car has only 27000 miles so hopefully nothing major there

perhaps your car needs a software update on the ZF gearbox....  
L 405 2013 FFRR 5.0 SC
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Buckblue I don´t won´t to scare you but go and see your stealer. I know that kinde of sound can come out from the differential (the one which transferes the power from the front to the rear axle). If a differential is loose it can make a sound like that and the sound comes out from under the cool box/gearbox. I hope I am wrong but if it is you should visit your stealer as soon as possible becuse worst case scenario the differential (and the axle which connects it) can end up if driving fast on a highway in your cabin-that is what my stealer told me. 2008 RRS TDV8 HSE, Java black, Alpaca,.....