Pretty sure that I know the answer but amazingly, this is the first time I've ever had to deal with one in my long career of taking things apart! The patient is my 2010 VW Jetta Tdi 6-speed manual with 170k miles, the last 40k or so of which it's had a bad rattling sound while idling in neutral with the clutch not depressed.
I finally got it apart and the flywheel has movement, (and a sound), between the two pieces but is not broken, i.e. the two pieces are still connected and the clutch functions correctly while driving. What on earth holds these two pieces together? Rubber? And why aren't they separated from each other??
I made a short video, not sure why I can't imbed it:
https://youtube.com/shorts/2A_nNK3B8O0?si=mPAe2DOYU5hg915X