Low frequency pulsing and humming signal:
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Morse code, SOS signal reception
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Pink noise
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Location alert, Radar
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SOS signal transmission, Morse code
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Electronic signal
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Horrifying throbbing low-frequency rumble
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High frequency signal
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Low frequency electronic signal
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Electronic signal, energy buildup
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Brown noise
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Morse code transmission
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Welcome, Morse code
★★★★★