For believers in the paranormal , unsettling sensations brought on by old buildings can be a sinister hint of loitering spirits. But new research points to a more mundane explanation: inaudible sounds from aged pipes and boilers. Scientists investigated the impact of infrasound on a group of volunteers and found that even though it was beyond the range of human hearing, people were more irritable and levels of cortisol, the stress hormone, rose when the sound was switched on. The finding suggests that even when people are unaware of the presence of infrasound, which can come from old pipes, boilers and ventilation systems in basements, the inaudible waves may still affect how they feel. On its own, the effect is unlikely to persuade anyone that a house is haunted, but for the right person in the right situation – a believer in the paranormal in a gloomy old manor, say – the unusual sensation may fuel suspicions of paranormal activity.…