The engine is 100% stock and TBH I'm a very careful driver as I like to save petrol, so it is hardly under a lot of strain.

I carried out the clutch work myself and I used the car on a daily basis for roughly 1300kms (short journeys and a 600km trip) and the car showed absolutely no signs of malfunction.

This issue occurred about three weeks ago after working underneath the car in order to open the bonnet (release mechanism had literally snapped!) the noise started as soon as I moved the car from my workspace (I had used the car a few hours prior to this event and everything was perfect), it's probably just a pure coincidence and I cannot recall even going near the gearbox, but I guess anything is worth mentioning...

The whining noise sounds very similar to the sound of straight cut gears.