I have a 1974 CB750 that is stock standard. However it does whine in third and fourth gears only. It's not really bad but is noticeable compared to the other three gears.
The bike shifts fine and has no other gearbox problems. It's travelled about 35,000 miles.
I assume it's wear on the gears themselves. If so, will they wear further quickly or is it something I can worry about in 10,000 miles time ?