sudden whistle (6th partial)

[Dorothy A. Bell]

Dear Friends,
I have been informed that a small Asian (Hazelton/K&C) piano that I had
seen two weeks ago has developed a "funny noise," and indeed it has: I
can hear over the phone that when C#3 is struck, G#5 sounds, almost as
loud as the fundamental. It's only on that note, and "it happened right
after you were here."
When I was there I tuned, regulated strike and letoff, removed the
action and lubricated flange pins with Protek, and eased keys at the
front pins. It all seemed unremarkable to me, and I didn't hear any
6th-partial ring on C#3.
What have I done? What has the piano done? What can I do? Questions of
strike point come to mind, but I don't want to start fooling with that
just on a whim, and why would it have changed anyhow.
Many thanks for any ideas --

Dorrie Bell