My wife's MK1 53 plate developed the gearbox whine at about 75K, my identical 53 plate was used for longer journeys in mainly higher gears and had still not developed any noise at all at 120K when I traded it in. The lower gears and acceleration put more strain on the bearing ( it is normally first or second gear that fails first in any gear box ) so it's back to the old truism that short local journeys are worse for car than motorway miles. Helical ( gears with skewed teeth ) are quiet running but put end thrust on the shafts in gear box, this thrust is greater in lower gears and will cause bearing to degrade sooner, straight cut gears do not generate end thrust and are stronger than helical, but are noisy - listen to reverse gear noise or the audible gear noise on BTCC or rally cars.
The bloke who fixed my wifes gearbox showed me the noisy bearing ( only one bearing is affected ) and it spun freely without any noise, it is just slight pitting the race that makes the noise, and noise is worse when end thrust applied by helical gears pushing the balls against side of groove rather than running on the deepest part of race. Bearing will not fail, but when you run out of volume on the radio you may want to get it fixed.
