<html> Roger, The Damper upstop rail slapping on the belly rail is a good candidate. Hardened guide rail felt is another possibility along with the damper head itself being a bit loose on the wire. Hmmmmmm... Jon Page At 11:50 PM 12/02/2000 -0600, you wrote: <blockquote type=cite cite>Hi John,           Guess we could be grasping at straws, but a couple of other things to try. Is the damper guide rail secure to the belly rail? If the board is flat in this area, that can cause some thud like tones. Measure the bearing with a compound gauge, and check the board for some curvature. If the glue joint on the inner rim or belly rail is loose similar result. Take an artist pallet knife, (.010" thick) and see if you can find any looseness between the board and liner. Just some thought's Roger John D. Chapman wrote: > > Remember THUD? > Here is the history.  I had not seen this piano until last month. > While tuning I noticed that notes 50, 51, 52, and 53 (top four notes in > agraff section,  just below the treble break) had an unpleasant > knock/slap sound, the same percussive knock which is in the background of > all piano tone, but in notes 50-53 it dominates the tone.  These are the > four notes between A440 and the treble break.  The orchestra conductor > asked me if I had noticed those four notes, as did the pianist, so I knew > it wasn't just my imagination. I have checked it out both upstage and back > stage (wood floors), and back at the dealership (concrete floor). >         Here is what we have done so far: > 1.  checked hammers for loose glue joint, flange pinning, and screw > tightness, > 2.  visually checked the action frame joints between notes #53 & #54, > 3.  checked the wippens for sufficient felt at the front to keep the > jack from slamming into the rep lever, > 4.  checked key frame bedding, front, back, and glides, with and without > damper pedal, and with and without shift pedal, > 5.  pressed down the back key frame with a long screwdriver to see if it > was slapping up against the dag, > 6.  played notes with dampers held all the way up by hand and by pedal, > 7.  moved the action in and out to see if the tone improved, > 8.  switched some hammers from the octave below to see if it could be the > hammers, > 9.  switched some whippins from the octave below to see if it coulb be the > whippins, > 10.  seated the strings, > 11.  applied firm pressure on the bridge cap at the end of the section to > see if there was a loose glue joint between cap and bridge body, > 12.  checked for clearance between the bridge and the plate, > 13.  checked for loose ribs, > 14.  checked for clearance between nose and bell bolts and soundboard, > 15.  checked that the bell bolt nut which was one turn past finger tight, > 16.  checked for foreign object lodged between soundboard and frame, and > between soundboard and plate, > 17.  tightened the end screws of the diagonal plate bar, which could be > turned another half turn to snug, > 18.  checked key leads and underlever leads, > 19.  checked the key bed with a straightedge front to back.  I found that > the board just beyond the board on which the balance rail glides rest was > high.  Chalked it where it passes under the front to back board of the key > frame which is just under notes 50-53 and found that is was just barely > touching. Sanded key frame there until there was adequate clearance. > Playing the note by pushing up on the whippin from underneath with my > finger without moving the key still produces the THUD, so I guess that > eliminates the keyframe anyway. > > None of this has changed the THUD. > What have I missed? > Why these four consecutive notes  with no sign of the problem above or > below them? > > John Chapman RPT > Wake Forest University > Winston-Salem NC </blockquote></html>