http://www.youtube.com/watch?v=vqTxWrUx5CY

Has anyone any ideas what this problem is on pianokey D sounds to me like a speaker vibrating but they all seem ok

Sounds like a room resonance issue. Try moving the piano to a different physical location in the room. See if the unwanted sound disappears, or starts occurring on another note (or notes).

I had a problem with extraneous vibration when playing through the speaker system. Lie on the floor under the piano and slap as many things with your hand that you can possibly slap. If you hear a resonance you don't like, you might have found the culprit.

There's a plastic cover hiding some of the electronics for the pedal unit. I removed it, added foam at strategic spots, and replaced it.

That's how I solved my problem.

Few days ago, I heard a similar resonance in my Kawai CA 63: it was the power cord that was not firmly attached to the socket and was causing that caracteristic sound (only with one key). You'll have to become detective and find the object that vibrates at that frecuency.

I have a fan set up close to my CLP 430. When the fan is switched on, some, and only some, notes sound funny on the speakers, but fine on the earphones.