Infrasound frequencies may subtly spike your cortisol levels. Credit: Deposit Photos Get the Popular Science daily newsletter💡 Breakthroughs, discoveries, and DIY tips sent six days a week. Every day, you encounter sounds that you can’t technically hear. Some of these are produced at incredibly high pitches, but many others occur as infrasound. This range of ultra-low frequencies below 20 Hertz (Hz) are found everywhere—during thunderstorms, inside factories, and even amid rush hour traffic. But a growing body of evidence suggests that infrasound is regularly detectable in spookier situations. More specifically, the seemingly imperceptible tones may frequently show up in “haunted” hotspots . This isn’t to say that ghosts generate ultra-low rumblings like crocodiles. Instead, researchers writing in the journal Frontiers in Behavioral Neuroscience suggest that infrasound may help explain why some places simply feel more creepy or foreboding than others. “Consider visiting a supposedly haunted building.…