The source of the rhythmic knock at the top of the engine is the hydrocompensator of the valves. This knock does not indicate a malfunction, but is a design feature of the engine. The chair only appears on the cold engine, after three or five minutes of hydro-compensators are warming up, and the sound is operating normally, and the sound is gradually disappearing.
A similar knock may occur due to the entry of small stones into the GRM-belts, but in this case the knocking is localized to the side of the engine from the side of the belt.