I have a Yamaha CLP-155 and I love the sound and feel BUT it has recently developed a very noisy key action when the keys are released - a loud thump or knocking (especially bad on the black notes. It sounds as though the felts have gone. My initial enquiries lead me to believe that the felts are unavailable for this model. Is that true? Can nothing be done to rescue this instrument? I am not happy that an instrument from Yamaha has become unusable when everything else is working beautifully. The waste is scandalous.