Good day,
since some thousand of kms, I can hear a sound coming out when running, I give gas.
The sound is like a sort of bzzz in sixth, fifth, fourth and thirth shifts (but in thirth has started just lately, it started in sixth and fifth, developing in fourth and thirth).

It does it only when I give gas, and I must be on the street, not on central stands. So under effort.

Since it comes out of shifts and defending by the shift, I guess it's not the clutch. Could be worn gears? Or what kind of supports that's going out?

My cbr it's a 600F 1999, atm has 68.000kms (42.500 miles).
Shifts changes without problems, clutch sounds and plays ok. Just the sound (that's pretty evident).

Any idea will be welcome!