993 gearbox noise

[Andre P]

American spec gearbox, had it rebuild with shorter gears from Guards Transmissions, GT 3 L/S from same co. I now can hear a slight diff whine & also when the gearbox is in neutral there is a nose in the box, when I engage the clutch the noise goes away. 50000 miles on the clock. Result I don't drive the car a lot, is it serious can it cause more damages on the gears as I don't want to pull motor & box again