Today's Puzzler

[Phil Bondi]

I'm guessing this puzzler is aimed more at the people who haven't been doing
this for a long time...people like myself..here goes:

The piano in question has history of tight jack flanges..when the call came
in, the caller wanted me to change all of them..I convinced him to let me
take a look at the problem first.

Sure enough, the one symptom of a tight jack flange(hammer buried in the
hammer line..key doesn't work) was exactly what the caller was
seeing...but..

it wasn't a tight jack flange...what was it?

First correct answer receives a slightly used white felt mute...! .. no,
that's not a hint.

-Phil Bondi (Fl.)
tito@philbondi.com