Noisy 'D' strings

[Lew Jones]

A four year old Steinway 'D', on stage at an area University has a
situation on which we invite comments.
Note 21, F (1st steel string unison on the treble bridge), sounds as if
the tone is being modulated at a certain frequency (about 12 Hz).  The
three strings of the unison sound very nearly alike.  The unison is
tuneable but at best has a slight beat (vibrato or tremolo).  It sounds
as if this unwanted frequency is being generated by a fan or some such
in the air moving equipment, but this is not the case.
A 25 year old 'D' on the same stage has not displayed this same
condition,

Lew Jones and Joe Brown
lewjone@prodigy.net