Something like this may explain the localized noise: https://www.newscientist.com/article/mg23431264-600-ultrasonic-speaker-lets-you-whisper-to-people-30-metres

Something like this may explain the localized noise: https://www.newscientist.com/article/mg23431264-600-ultrasonic-speaker-lets-you-whisper-to-people-30-metres-away/ https://www.newscientist.com/article/mg23431264-600-ultrason...