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My old digital camera makes a creaky D4 noise when the lenses open and retract, and it plays what's just flat of a B7 for its beeps, a very high note indeed.
Digital Camera
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Electric hum, mains hum, or power line hum is an audible oscillation at the frequency of the mains alternating current, which is usually 50 or 60 hertz depending on the local electric utility configuration.... Assuming a tempered scale with A=440Hz, a 60Hz tone is almost exactly halfway between A# and B two octaves below Middle C....So perhaps I'm hearing a 60 hertz tone in the electric hum of these motors.