Vrod gearbox noise

Hi I have a 2003 vrod with 4K miles on. It's started making a noise from the gearbox drive pulls about 50mpg the noise goes off when backing of the throttle and isn't there when cold. I have backed of the drive belt and replaced the drive belt plate on the rear wheel. I am thinking The gearbox out out shaft bearing is knacked because the belt was to tight when I got the bike? Can any one shed any light if it could be anything else? Kind regards
Ged