It occured to me that one way to see whether Petra's (and others) eartones were created in the brain but triggered by a real cause from outside would be to strap Petra into a mad scientist's chair and bombard her (or some other hapless volunteer) with all kinds of electomagnetic radiation....maybe some plain old radiation....until she hears eartones. I'd vote start with fluctuating magnetic fields.

The volunteer might have to donate their brain so that it can be checked for magnetite and anything else of interest.....but this could just be a loan.

If Petra is not willing to do this, she, and the others in her group, might hang out near high-tension-high voltage electrical transmission lines and see what they hear (hmmm...can you see what you hear?). I know from personal experience (magentic field surveys) that thse lines put out fluctuating magnetic fields.

I hear eartones but I'm not volunteering.

Chris