500AMG1283

Question for everyone. So I got in my ml today, and after driving for a bit i noticed a bit of a bucking in between the shift of 3rd n 4th (right about around 25-30MPH). At first it was so minimal I thought it was just bumps in the road, but as it went on it got progressively worse. I did some self tests to see what exactly was causing it, noticing that as i shifted the gears on my own the problem didnt really occur, nor during rapid acceleration did it occur. Just casual driving seemed to cause it. So, I ran it down to the dealer and I noticed as I got there it got even worse. They took it out for a test drive, couldn't figure it out, took it out again and came back telling me something's most likely about to let go, seeing as they heard all these different noises coming from it that were not there previously (along with the hard shifts). To describe it, it almost was like as when you come off the accelerator it shifted and than shifted back up again for a split second. Really weird . Anyone have a clue as to what this may be? I had to leave it at the shop, for fear of it breaking down, but I'm curious to get some feedback.