Engine knocking noise at 4000-4500 RPM only Fazer 600

[kutce]

I just got a 1998 Fazer 600 and rode around 350km on it.
I notice there is a knocking feel on the bike at around 4000-4500 RPM. Its not possible to hear snce its only apperant when driving and the wind becomes louder. It it possible to feel through your legs, hands and butt.
I have no idea what it can be
- Knocking is not present with clutch pulled in
- Knocking is not present at low RPMs
- Knocking is not present or not feelable at high RPMs
- at 4000- 4500 RPM very noticeable constant frequency knocks
- No rattle on the cam chain at idle
- bike start easily
- No rattle when decelerating
- Bike gargles from the exhaust when decelerating, dont know if its worth to mention


What can this be??
I want to check the carburetor syncing then cleaning, maybe one piston is not getting gas and it hits a natural frequency of the bike at 4000 RPM. Next would be to check the chain adjuster. Hopefully its not the cam chain.


Thank you for the help already