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Vic Tandy was in a workshop rumored to be haunted. He suddenly felt a chill and distinct uneasiness then saw a silent grey figure before it faded away. But the self-described "hard-nosed engineer" wasn't convinced he'd seen a ghost…even when a blade of metal he'd placed in a vise began to frantically vibrate on its own. In fact, that was his clue there might be a more natural explanation. Experiments led Tandy to a fan generating waves of infrasound—frequencies below the range of human hearing. Studies have suggested it can indeed cause eerie sensations in people, and it's produced by many things…including spooky thunderstorms. In this case, the ghosts left after a fan adjustment. With the National Academy of Engineering, Randy Atkins, WTOP Radio.