18kHz is inside the human hearing range, though at the far end. The ultrasonic sound in these mice experiments was 3.2 MHz, for 50ms duration, and pulsed 10 ti

18kHz is inside the human hearing range, though at the far end. The ultrasonic sound in these mice experiments was 3.2 MHz, for 50ms duration, and pulsed 10 times a second. Not sure if the 18kHz sound you were subjected to and this mice experiment are comparable in terms of effects. (but I have no doubt that a consistent 18kHz chirp would be quite unpleasant and draining).