Dear Richard
I own a ctx 9000. I'm a hair splitter too! I noticed the same noise at the middle C, the G below that and the C & E in the next Octave.
It is a mechanical sound of the metal spring hitting against the plastic key maybe? I noticed that it doesn't occur if you play the key softly.
Was thinking of returning the keyboard also, but went back to the store and checked other CTX models as well as ctk models and the sound they make is worse than my keyboard!
The yamahas are pretty silent though. The KORGS had some pretty bad grating noises too ( with the power off!)
Decided to keep my keyboard as it is. I suppose the sounds may get a little worse with wear and tear. The display pieces had almost all the keys with some noise or the other.
It is a purely mechanical problem though since it occurs even with the keyboard off. It doesn''t affect the keyboard speaker or outpur sound though!
