I remember reading something a psychic said. She somehow got involved with the case of a girl. I think everyone thought the young girl had gone mad. Turned out she was actually psychic and couldn't control her gift, so was frightened to death of what she was experiencing in her head.
The girl had gone to hospital for an appointment and had picked up the residual energy of all the trauma that had been there.
I've been told of psychologists/psychiatrists having the gift themselves. Maybe it was that and one of them was around and knew what was happening with the girl. She was making a lot of noise, she was so frightened, so probably drew a lot of people's attention.
What I'm trying to say is maybe that's what we're picking up in these places - the residual energy - and they're not all haunted.