This is known as self-rectification and can occur if the thing is near a strong radio transmitter.
You should check ALL your audio cables have good grounds. A broken shield on a cable can let in the radio signal which if strong enough can rectify (detect) and recover audio from an AM broadcast station. Note that some aircraft radios are also AM, You can also receive SSB type signals, however you will not get intelligible sounds.
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This is known as self-rectification and can occur if the thing is near a strong radio transmitter.
You should check ALL your audio cables have good grounds. A broken shield on a cable can let in the radio signal which if strong enough can rectify (detect) and recover audio from an AM broadcast station. Note that some aircraft radios are also AM, You can also receive SSB type signals, however you will not get intelligible sounds.