I've posted this before, and thought I had fixed it but finally discovered the solution: How do you get the beep to stay silent when you power the V-Synth on? The answer is you need to have Powerup Mode set to 'Last Set' in System Common Master screen.

If you have that set already then you should have no beep on power up (once you disable beep and save settings). If like me you had it set to 'Default' then the beep is back everytime you switch on.

So now I know,
B