On this grand piano, some jacks are rubbing on either sides in repetition lever windows. When keys are played, the rotating jack-rubbing-window motion creates big clicking like noise.
The jack center pins need to be bent to let top of jack centered to the window. Support bottom of center pin on hard surface on the side where the bend shall be, whack top of jack with a hammer till it is centered. In order not to over do it, not too much force needed for each whack. After a couple of adjustments, one could only find way more jacks to be whacked...
One this upright action, all sorts of clicking noise are present. Turns out that all the action screws are loose includes: hammer flange screws, wippen screws, and damper screws.
From left to right, tighten hammer flange (butt) screws, wippen screws, and damper flange screws. Noise is gone after this process, took about 30 minutes. The piano owner was so happy, so did the piano technician ^ ^