loud transmission thump
 

I have a 2014, 300, v6, 41000 miles I just experienced this for the second on this car. I started the car put in reverse released the brake and tried to back up, nothing happened so I hit the gas pedal and I got a loud thump noise and the car started to move with no issues after that. The first time it happened I was going between reverse and drive, and we got a loud thumping sound. Has anyone had this noise, I'm assuming it drive train issues and would be under warranty, but what will dealer do about something they can't get to happen. Any advise would be greatly appreciated.
Thanks