Pianos are made mostly of wood and sometimes the wood can warp.
I am a full time piano technician " jackspiano" and there
are times when I have to do some creative woodworking.
The piano is a Bosendorfer grand and I am tuning it to A=440
using a Verituner app with an iPad.
The keyboard which is the keys and hammers has to be removed
so I can inspect the inside the piano....
With the keyboard out of the way I see that the pinblock is warped.
bottom of the pinblock....
The pinblock has to be planed down so there is enough clearance
for the hammer shanks. It did not take much, after around 20 stokes
with the plane I tested and it was fine.
Everything is put back together and the problem is solved, no
more clicking and the piano is ready to play. I don't know if the
pinblock will keep warping but this worked out, I will just have to
keep monitoring the piano.
Make a wooden hygometer French cleats on steriods Finishing table