I installed Pianocorder, PianoDisc and Pianomation players for
many years.  The problem was also sometimes when they were new.
Occasionally this ultrasonic pitch was being generated and few people
could hear it.  I could.  I found it is a vibration with some component
that was loose and vibrating.  Make sure all screws and nuts and bolts
are tight and this should take care of the problem.

This sound is not to be confused with the "zoop, zoop" sound of the
solenoids when playing softly.

Doug L. Bullock
http://thepianoworld.com/