Hi Mike, Two more thoughts after your clarification. Point one, the knuckles not solid in the mortice slot can cause this problem, they can appear tight but the only sure way is to pull one and reglue. Point two, those teflon bushings (hammer flange) can make a hell of a racket, with very little feelable motion, a quick check is to raise the hammers to the horizontal,let drop and observe the bounce. if there is more bounce than the other notes you have isolated the problem. Wippen flanges seem to be able to wear to a greater degree with out causing the problem that you have mentioned. If you switch the hammers first it will isolate shank from wippen as the cause of the problem. Have a nice day. Roger Jolly.
This PTG archive page provided courtesy of Moy Piano Service, LLC