Low-frequency rumble, high-frequency squeak:
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SOS signal reception, Morse code
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Location alert, Radar
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High frequency signal
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Horrifying throbbing low-frequency rumble
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High frequency pulsating electronic signal
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Low frequency pulsing and humming signal
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Pink noise
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Brown noise
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Reception, transfer, Morse code
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High frequency squeak
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Police radio
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Electronic signal
★★★★★