I stumbled on a reference to this story recently. Just as fascinating this time as when I first read it.
TL;DR: Apparitions & anxiety in a lab are traced to infrasound from a fan producing a standing wave resonating at the frequency of the human eye. Vic Tandy went on to investigate whether the same waves were present in at least some sites with haunted reputations.
He died in 2005. I couldn’t find much follow-up research in a quick search.
Ghost buster: Chris Arnot explains why Vic Tandy of Coventry University is doing time in a cellar