Nice video! 

I can't say I ever heard that exact noise...  could definitely be something vibrating as RT325 said.

If not exhaust maybe skid plate?

If you have a mechanic’s stethoscope start with the reed cage harbor freight has one for 5 bucks if not the redneck way is a long screwdriver against the cage and put your ear against the end of the screwdriver and observe the noise 

Check your engine to frame bolts just another idea I would buy the scope(I have one) and idle it up to the noise and scope everything to find it

Had some strange noises to track down over the years but a common one was the front brake cable singing when forks are compressed & let up as cable slides against the guide on the lower triple clamp.

Thank you for your comments , apreciate all your input
Skid plate, cables and clutch arm are not vibrating, i checked already.
Also the crank seal doesn´t touch the flywheel.
I slightly hit with a hammer on the flywheel nut, while motor running. No change in the noise.
Will check the exhaust, i have a spare one.
Good idea with the scope, i will buy one.
I dont think thats something serious, but simply annoing.