Low-frequency rumble, high-frequency squeak:
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Radio noise
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Morse code, SOS signal transmission
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Radar, location alert
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Pink noise
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High frequency squeak
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Morse code transmission
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Electronic signal, energy buildup
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Horrifying throbbing low-frequency rumble
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Morse code, transfer, reception
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Low frequency pulsing and humming signal
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High frequency signal
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High-frequency squeak, Low-frequency rumble
★★★★★