[SibSerge]

A couple of things from my own experience with the issues you notice.

1. Knocking turned out to be a bad clutch basket. These use rubber bushings in the basket and rubber just plain gets "tired" and hardens after 13 years. Many of the rubber pieces/components that I replaced on my 2007 were way harder than the new ones.
2. I had low compression in the right cylinder. it was showing 120psi vs 195 in the left. It turned out to be a small notch in the spark plug area luckily not on the face surface of the plug. That notch was not letting the oring to seal and it was leaking there. Lubricating the oring with heavy antiseize was enough to plug that hole. 205 psi was measured afterwards.

Just to confirm - you do open the throttle when you test and you did try to squirt some oil into the cylinder to confirm the rings are a/non issue ?

Like Danno said check the clearance of the valves first.