Here's the thing I was reading:
The biggest culprit when it comes to ghostly sounds and sightings might be infrasound, low-frequency sound waves below the range of human hearing, that can nevertheless have tangible effects: feelings of nervousness, for example, or hyperventilation, or even a sense of another presence in the room. There's even speculation that these sound waves vibrate at the resonant frequency of the human eyeball, causing visual hallucinations.
Vic Tandy was a strong proponent of the infrasonic theory, and even pegged the specific guilty frequency -- 18.9 Hz -- before his untimely death in 2005. Officially, he was affiliated with the school of international studies and law at Coventry University, but he was also the unofficial "chief ghost buster." (Perhaps Bill Murray will play him in the film version of his quest.) He wrote two papers for the journal of the Society of Psychical Research: one citing infrasound as the cause of a "haunting" in a laboratory in Warwick, and another citing infrasound as the source of a "ghost" in the cellar at Coventry Cathedral. Lots of otherwise sane people felt uneasy descending into the cellar, sensing some kind of presence, and occasionally -- as in the case of a visiting journalist -- seeing the face of a woman peering over their shoulder.
As for the Warwick laboratory, Tandy himself worked there, and could personally attest that the effects of infrasound feel very real indeed. He was working late one night, and suddenly felt the hairs rise on the back of his neck. At the same time, he caught a glimpse of a gray apparition out of the corner of his eye, that disappeared when returned to face it. The culprit? A newly installed extractor fan. "When we finally switched it off, it was as if a huge weight was lifted," he told the Guardian in July 2000, and he suspected there may also be a connection between infrasound and "sick-building syndrome." I have a strong suspicion that Ernie the Ghost's spooky effects were at least partly due to something like infrasonic vibrations from that old mainframe -- because when Terry and her colleagues got rid of it, the "ghostly presence" disappeared. Regardless, Tandy died before he could complete his investigation into why some people are affected by infrasound and others, apparently, aren't.