For survey purposes - I have a nice clack too and suspected the flex plate but it shows no signs of cracking. I do know that there was a thread on here a while back showing pictures of a broken flex plate. It looked pretty gruesome.

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TC
Current stable:
- 2004 Mazda RALLYWANKEL
- 2007 Saturn sky redline
- 2004 Explorer...under surgery.

Past: 135i, GTI, 300E, 300SD, 300SD, Stealth