Could this possibly be the string resonance that Casio has tried to emulate in the piano..to give another dimension to the sound..perhaps your hearing is tuned into the resonance frequency and you hear it more acutely? I would try running the sound through a mixer with as many equaliser channels as possible even a graphic equaliser turning down the higher frequencies in small increments until you effectively find the frequency that affects the sound directly and turn it down to achieve the desired effect..just a thought
Can someone please tell me where to download something other than the basic manual that came in the box. As good as it sounds it's not exactly the most obvious operating system! Any material that shows me how to build layers, get drums to play drum grooves etc.thanks