Welcome. It sounds like you could have the start of the dreaded input shaft bearing syndrome, which effected Mk 1 models of that age. With the engine running and the car in neutral, can you hear the noise? If you depress the clutch, does it go away? A noisy clutch release bearing only makes a noise as you activate the clutch, so it isn't audible when the clutch is not actuated. The gearbox input bearing is.
The good news is it will not fail. The bad noise is it will get steadily worse.
I took my car to a reasonably local Gearbox specialist (
http://www.topgear.uk.net/home.html) and they replaced all the bearings and seals, with the gearbox in situ, for £324, which included parts and VAT.
My local garage quoted well over £1,000.
The car is now like new. I have since done 6.000 trouble free miles.
Best of luck.