buzzing on piano

[Tom & Sharla Zasadny]

Greetings,
What would be the origin of a buzz on this 1930's Steinway Model "M"  that 
seems
to be soundboard related and acts like lthis:  It has been present for a 
couple of
years; less in the summer and more in the winter and at F5only.  It is more 
wooden
than metallilc in quality and is more pronounced with a harder key blow.  E5 
was
pitched up to the F5 pitch and caused the same buzz.  F#5 was tuned down to 
F5
and also caused the buzz.  Pressure over the bridge, movement of the duplex,
movement of the strings under the capo, pressure over all ribs and over the
soundboard top and bottom, tapping the bridge pin down and increasing its 
angle
availed nothing. The soundboard has no cracks and bearing is good with good
sustain.  Visual examination with light and mirror under the plate showed 
nothing.
High air pressure through every opening was not productive as well.     
Muting two
strings at the F5  quieted the buzz.  When only one was muted, it returned 
though less
than with three singing strings.  If I struck two singing strings, the buzz 
equalled that of
three strings with a less forceful blow.  Now here is the only diagnostic 
clue I can
give.  When the plate bolts were tigtened the buzz disappeared though for 
only 15
minutes.  (It came back as I was doing some regulation testing.)  I 
tightened the bolts
again and it was quieted for a short time. Tightening again (I put overly 
heavy torque
on this last time) lessened the buzz at F5 but it turned up at C6.   Soon 
the buzz
became strong at C6 and remained small at F5.  I checked for glue along the 
entire
inner rim at the soundboard junction and I eliminated all action and 
environmental
sympathetic vibration questions. What is this?  How do I fix it?  The 
customer is
piano professor and accomplished performer.  He is ready for this to be 
history.

Thank you friends,

Thomas N Zasadny
(home)1(319)-934-3552

_________________________________________________________________
Get in the mood for Valentine's Day. View photos, recipes and more on your 
Live.com page. 
http://www.live.com/?addTemplate=ValentinesDay&ocid=T001MSN30A0701