I had the same problem, but I had several of them too loud, and it was getting worse. The cheapest, most effective way to fix it is to take a Phillip's screwdriver and take apart the frame, the sides may not screw on but instead may pop out. The keys snap in, so take them out, one octave at a time, starting with the white keys. Keep them in order; don't mix them up. Clean the little rubber contacts underneath them with a Q-tip and some rubbing alcohol. Be VERY careful of any ribbon wires, they are delicate. Do not press the rubbers too hard, clean them gently. When they are cleaned, snap them back in and clean the next octave. Don't just clean the ones that are loud, because the others will be getting loud soon, if one has already started. Good luck! Don't end up with extra screws!