Ours does the same thing! A loud bang with severe hard jerking. Never completely stops. Had it in the shop once and they just said the transmission fluid was low. I was assured it wouldn't happen again. Well, it did it again yesterday. Needless to say, calling the dealer in the morning. Going to have my husband check the fluid. My BIL, who teaches automechanics, said he thinks it's something to do with the transfer box for the AWD. I'll be mentioning that to them when I call. This stinks because I want to love my new car....but I don't!