YamahaP125 keyboard, all keys work but some (middle section) were sometimes very loud. Disassembled , vac, removed centre rubber strips, carbon looked good, lightly tip/alcahol reassembled. Better but when 3 keys played at (same time) “The lady” says sounds off??? Any suggestions?
Have you tried altering the key sensitivity settings?
Which keys are affected?
I think you are looking at resonance based effects causing it to “sound off” (whatever that may mean). I was at a site not that long ago where one YAMAHA P-145 was in an empty room in a wooden house (Queenslander) and the owner was complaining that some notes sounded louder than others - because these notes hit the resonance of the room.
You may have to go on-site to assess