Might have more than one issue.
The 2nd being the clutch dragging a bit. Is the clutch cable adjusted to 2-3mm free play, as per manual?
This is very important. E.g. 4mm will not do.
if you check this and find it needed adjustment, best go for a spin after and see what impact it had.
Also verify if the noise changes or goes away when decelerating in gear and pull clutch lever in.
If noise remains then it could be from the trans e.g. output bearing given age of your motor.