A really good mate of mine, and his family (wife, eight month old kid) left a house purely because of 'things' happening. Regularly. A shadow would pass across the hall almost daily. Saw that myself several times. Voices, whispers, and sometimes screams were heardfrom the same empty room. Said room was continually cold, even with central heating on.
These are well educated, calm and reasonable people, but couldn't explain or put up with it. Ghosts? I, even though I saw the shadow, (That did look almost solid, but 'shadow' is the best word can use to describe it) am reluctant, as are they still to call it such.
They brought in a guy to investgate it while they were there, and his attempt at an explanation, for their 'problem' and other 'ghosts' he has investigated, was the theory that in houses, buildings, or places, where there has been some sort of extreme trauma, like abuse of a child, (or adult) or in many cases a murder. The intense 'psychic' power that is possible in all minds can leave 'impressions' in the walls, floors etc of where they took place, like images on film or videotape. And, some, not all people are on a similar 'wavelength' psychically (sp?) speaking, and can cause these replays.
The house was in a small Wiltshire village, near Devizes, its a very old cottage, and though they couldn't find any record of anything that had happened there as public knowledge. All they got of anything of a possble sinister story, was an old guy in the cottage opposite said his mother used to say the people who lived there just before the first world war, claimed their seven year old boy simply ran away, and because the war happened, no real investigation was done, not enough police etc. The father never came back from France, and the mother died there alone some years later. Nothing was ever heard of the son again, even though some attempt to trace him was done by solicitors acting for the mother to sell the house after her death.
Interesting theory to 'ghosts'.