Hello Mark,
I too have a very load Middle C note on a Piano sound when the touch sensitive is at a manufactuers setting
Initialising the keyboard puts the touch sensitive at number "6"
If I change the touch sensitive to "0" all notes play at the same volumn .

I presume I will have to dismantle the KN7000 to spray the contacts of the offending note with a contact cleaner.

Dave L in New Zealand .