Do you think the noise would go away when driving and just be there at startup? Sounds unlikely to me but I'm not quite familiar with what it looks like.
Um.. actually, no.
But he wants to separate the engine and gearbox on the assumption it is the flex plate, and I'm just saying that it is easy to check first, before committing to all that work, speculatively.
Pugwash has some good suggestions, particularly "check the simple things first".