I can heard a distinct rumbling sound when idling in neutral which I presume is coming from my OD gearbox. The sound stops when I depress the clutch which I guess confirms it's a gearbox bearing, probably the front. The sound stops because the gearbox stops. I guess I'm looking for confirmation of my diagnosis and whether I should be overly concerned and replace this bearing ASAP or is it likely to be a mere annoyance until I can 'get around to it'.