I read the other thread and I felt I shouldn't bring it from the grave. I only notice this when I back the car from the garage and come to a stop before going forward. It is a very metallic clunk. It sounds like its coming from the rear passenger side but I am. not 100% certain. It happens when I actually stop before switching to drive. It is a 2013 Two. 30,000 miles on it.
Are you seeing any computer codes? I'd get this checked out, as it sounds like the noise my 2005 made when the transmission failed. While trans failure is rare, it does happen. Your car is under warranty, so take it in for a check up. Better now than later, when you are stuck on the road.