chiffing attack sound in bass

[Robert Bussell]

I have been asked by a pianist to voice out an attack sound she hears in
the bass. The best that I can describe the sound is that it is like the
chiff a pipe organ makes with the note starts.  I have heard this sound
many times before in other pianos of different makes but have never been
able to solve the problem.  This is the first time that  a pianist has
brought it up.  It is not string leveling or hammer to string mating, shank
and hammer glue joints are good,  pinning is good, shape of hammer looks
good.  I have tried switching out the hammer and shank with other notes
that don't have the sound and it follows the hammer.  Another technician
suggested that the hammer has been over voiced and to use a couple drops of
acetone and keytop on the strike point.  This gets rid of the chiff sound
but then to note is too bright.  When I lightly file off the crust and
needle the surface to even out brightness the sound returns.  I would
appreciate any suggestions.

Bob Bussell