Couple of things Lowell...Can you describe the pitch of the tone. I am a musician and also have perfect tuning...Could you describe the tone in respects a middle C note on the piano which is used for tuning orchestras...either that or the oboe or the first violin...but it usually is a middle C. If you had a pitchfork, which are not expensive, you could compare the tone to middle C at least higher or lower.

If others think this common EQ precursor is valid, and I do, then what might you suspect is the mechanism... Is it sound waves or electrical waveform?