Ping went the strings

[robert sadowski]

To the list:
     
     I just tuned a 1958 Steinway L that has the "ping" problem.  You turn
the hammer to lower the pitch and nothing happens.  Suddenly a "ping" sound
is followed by a 10 to 20 cent drop in pitch.  This piano had the problem
in about 75% of the aggraffe notes.  Some notes are immpossible to tune .
It was maddening!  I'm assuming the strings have a nick that is getting
hung up in the aggraffe holes.  What's the cause and any solutions? 
Thanks, 
Bob Sadowski
Erie, PA. Chapter
rob@erie.net