Gearbox rattle

1960 Invicta 401. I've got a rattle, which sounds like a loose clamp on the exhaust or perhaps a baffle gone.Thing is, it's neither of those, it seems to be a transmission thing. Anyway, it happens when the car is idling and disappears when I pick up the revs. Also it doesn't happen straight away, the engine need to warm up first. I've got the engine out at the moment and there's no obvious cause (eg loose metallic object in the bellhousing etc) There is some sign of wear in the central hub on the torque convertor, but the torque convertor is not rattling when I turn it by hand. Also, shouldn't the torque convertor just pull out? This one just moves about an inch & then just stops. Anybody got any ideas?
Thanks