All keys making a C sound

[McGintyMuse]

Press a key – any key – and there is a dink on C above middle C.

This happens without any sound output – no amp, no headphones, no nothing.

I originally thought it only happened on the release of a note or chord, but today I touched the keyboard before turning on the amplifier and there it was. Every key has that wretched dink.

If I have the amp on, I hear the correct note or chord and then the dink immediately after. And it's driving me crazy!

Does anyone know a fix for this? Or a repairman in the Phoenix, Arizona area?