gearbox noise

Hi,I am hoping that someone can offer me some advise,I have rebuilt a gearbox on a 1954 series 1 due to the layshaft had snapped!! So i have replaced the layshaft with new bearings and put new oil in,Re-fitted the gearbox and since then i am experiencing a whining sort of noise,but from what i have noticed the noise seems to disappear in fourth,
Has anybody out there experienced this or know what could be causing this annoying noise.
The noise is more apparent outside the vehicle.

Cheers
Pete

Did you check for end play in layshaft.. If it was present could be caused by worn sleeve behind 3rd gear and will need replacing.