Sounds about right... I've head bearings do that. Some times it rattles and other times it doesn't.
Assuming it is the release bearing, it is isolated from the gearbox, so the oils, etc. won't have any effect on it.
As I say, assuming it is the release bearing, I wouldn't worry too much... the noise will come and go and one day it will probably fail. Depends how keep you are to change it.
Once you have gone to the effort of splitting the engine and gearbox apart, it is worth (IMHO) replacing the clutch assembly too, so the longer you can leave it, the better in many respects.