. . . Whenever a key is pressed -- and it seems to occur with every key, though some more than others -- there is a fairly loud humming noise over the top of the played note. It has a sort of metallic character to it, though I'm unsure if the source is physical (something resonating where it shouldn't) or electronic. The effect of this noise superimposed over the notes is very unpleasant to my ears.
I didn't hear anything peculiar, but my hearing is badly compromised above 4 kHz or so. Why do some people hear something funny,, and others don't?
So here's an idea:
All the strings in the top octave of the piano (sometimes more than the top octave) are _undamped_. They are free to resonate with the overtones of lower-pitched notes.
If you play an acoustic piano, striking keys in the lowest two octaves staccato, and listen carefully, you'll often find that some notes ring, fairly loudly, after you've let the damper fall. The ringing isn't at the pitch of the key you struck, but at a much higher pitch. You might hear that as "metallic".
What's happening is that the overtones of the note you struck, excited one of the undamped strings, and that _undamped_ string is ringing.
. . . This is expected behavior, although people don't mention it often.
Your Kawai has a "sample-based" sound generator. That is, somebody recorded the sounds of a _real_ (acoustic) piano, and when you strike a key, the DP plays back the recording. (It's more complicated than that, but we only need the basic principle here.)
. . . If that original acoustic piano had a key with a sustained resonance,
. . . that "ringing" will be captured in the sample.
. . . And when you strike that key on your DP, the "ringing" will be
. . . faithfully reproduced.
I've tested earlier versions of Pianoteq (which is "model-based", not "sample-based"), and sure enough, it's faithful to that behavior:
. . . Some bass notes have sustained (but faint) ringing in the high treble.
When the stars line up right (or wrong), and a bass or mid-range string has a strong harmonic that matches the pitch of one of the un-damped high strings, that string is going to sing, un-damped.
I don't know if that's what you're hearing, or not. I don't have your ears, and I might be deaf to a sound that's really present.
