inquiry/diagnostic

I hear a slight whining or sounds like a bearing when accelerating or decelerating on 4th and 5th gears only. and starts at 2,000 rpm and up.

when on steady throttle (any gears) or from 1st to 3rd gears on any rpm theres no noticeable sound.

the whining sound or vibration increases as the rpm increases. its like its connected to the rpm. when clutch is pressed, no sound. coasting on neutral, no sound.

any ideas guys if this Is a big problem? or what should I be checking?

its a jimny jx 2009 manual tranny. at 80,000km

-have also posted on Suzuki jimny thread.