[Bassman]

I have a 2006 3200 Open with Cummins, yesterday I was underway and started to hear a high pitched electronic sound. I tied up killed the engines, still heard it. Turned off the electronics, still heard it. Checked all of the breakers/fuses still heard it. The only thing that worked was to shut off the batteries. I did this several times and every time I turned the batteries on the sound would come back, not an alarm just a tone. After several minutes I started the boat again and it went away. Everything seems fine with the systems on all fronts and the boat ran fine.

Any thoughts on what this may be, it sounds like it is coming from behind the dashboard.

[Sans Peur]

There are several thing behind the dash that may make noise. High water alarm, oil pressure, water temp, even your GPS . If something is getting a little weak it may allow a small amount of current to go to the piezo alarm. This will make it a muted sound unlike full voltage going to it. Since you switched off everything one by one and only a full disconnect of the batteries seemed to work I would look at systems that are usually wired directly like the bilge high water alarm.
Also look to see if you have a co or smoke alarm wired in. I had my co detectors getting older and they would sometimes go off. A couple of times one of them would just kind of chirp a few times.