Thanks for increasing your description of the noise it really helps. The flexplate bolts to the rear of the crankshaft and it is like a flywheel. (not quite) Your torque converter bolts to it. Some inspection is possible from under the car. There should be a cover you can remove. You rotate the flexplate to inspect each bolt and try to look for cracks.Not uncommon to have loose bolts from the flex plate to converter or cracks in the flexplate. Again my knowledge on mercedes is very limited. Archives under flexplate or even torque converter might help you more. If you can safely get under the car ideling in neutral you just might locate the exact source of the noise as well. Emergency brake and blocked wheels as safety is first. Also since you are leaking fluid. The back of the torque converter has a coupling that slides into the transmission. If the oil is red you might be looking for a problem in that area. You might be faced with pulling the tramsmission. But again do check the archives and wait for others to respond.