Hammer noise.
After clicking on the image of the piano which goes away to make room for a settings screen, under VOICING (top centre) you will find Hammer Noise: here you can cancel the mechanical noise of the attack

You can also do this for each individual key by clicking on Note Edit at the top right of the Pianoteq main window, choosing Hammer noise from the menu: a screen will open where you can see the value for each individual note

Great, thanks. I have realized I need to upgrade from Stage to Standard to get these settings.

Addition: have upgraded Stage to Standard, and yes, everything OK now. To my taste reducing Hammer from 1.0 to 0.30 is close to be optimal.

You can also do this for each individual key by clicking on Note Edit at the top right of the Pianoteq main window, choosing Hammer noise from the menu: a screen will open where you can see the value for each individual note

Stage 8 is in use with Kawai asd Bosendorfer. How to reduce mechanical knocking? I mean the attack phase, not the release phase (have found for the last one only). The thing is, SL73 mk2 has got own rather noticeable knocking. Doubling the effect results in obvious  exaggerating.