What causes gearbox whine?

[thegreenman]

thanks inadvance for looking and helping. What are 4 main/most common causes of gearbox whine.

 

[thebax2006]

The 2 bearings on the input shaft and the 2 bearings on the main shaft.
Turn up the radio or buy a used transmission from the bone yard.

 

[LeAnne]

Straight cut gears always whine - that's why reverse in most manual transmissions is so noisy.
If the transmission whines in all gears, I would suspect a bad bearing.

 

[bandit_60]

they do whine in reverse. check the fluid.

 

[AberdeenTyke]

Layshaft bearings, common on old British Leyland cars in 4th gear, notably the Allegro and Marina.
There's your 4 answers.