I flooded mine on sunday and when it did the odd fire I heard this horrible clunk noise too, its not long ago that I built her up. theres nothing on the sump plate regards shims like there was a few years ago but I do intend to investigate end float when changing the gearbox in the near future, I do know the metal on metal sound is a horror to hear you have my best wishes on finding a cure or reason for this and I hope I get an answer regarding my CLUNK , ime hopeing its not end float because a got that to about 1 and half thou.