The most common causes are: Poor Old Felt. Replace with better felt, maybe Yamaha. Poor felt location Re-position the felt. In case two mute off all strings except the worst offender, remove the damper felt and replace the damper but set the lever height too high to lift the damper except at the very end of key stroke. Cut two standard length felts and slide them under the block and leave about 1/8" sticking out at both ends. Play the key. Continue to move the felt in and out until you get the most effective damping possible. Carefully measure the locations of both felts. If you cannot find the best location then try using longer or shorter felt pieces and move them back and forth. Eventually you will find an optimum length and optimum location for those felts. This should take about an hour or less. Remove all the dampers, make a gauge or jig to help keep the felts perfectly located for visual effect and replace the felts. I have had this problem on a Knabe and on an S&S B. Lots of luck. Newton
This PTG archive page provided courtesy of Moy Piano Service, LLC