Two things to look at:
One change gearbox oil. It gets forgotten, will be ancient and as already mentioned may be way below the level.
Also, the magnet on the drain plug will have picked up any swarf which is good to get rid of. Not a very difficult job, takes longer to get the panels off than to do but the drain is very close the the subframe (by the wish bone mount) and you may have to gently jack the box up half an inch to get a tool on.
Two clutch slave cylinder: as they fail they actuate inconsistently so the cluth isn't fully dis-engaged. (Do you sometimes have a couple of goes to get reverse? or clutch goes the floor and doesn't pop back up, when you are driving enthusiastically?) £25ish for the part and not difficult but an Easybleed is a very good idea as they don't self prime. Give the whole thing a really good bleed.
The whine is probably the clutch thrust bearing but that's a gearbox out job so its best to do these two first as they are cheaper and easier and the whine may be reduced even if it doesn't go away.
GTV and Racing Driver