I think I know what you're experiencing with the low-speed clacking noise while in gear. I went from a dual-mass flywheel to single-mass (like you have) several years ago and started experiencing that. All mounts and bushings were/are fresh and tight, but could not eliminate it. Kind of like a "trailer-hitch" effect, is I believe how lookforjoe described it, with a metallic clink. I finally discovered that there is just a small amount of rotational slack in the axle itself. Not sure if it's where the splines meet the gearbox, or if it's internal in the m56h itself. Either way, it's not going away. My m56h was already rebuilt two years ago, so it's just a part of life. I believe in my case the dual-mass flywheel was absorbing that slack; it only became noticeable when I converted to a SMFW.