Poltergeists are mostly seen as psychokinesis activities, the paranormal way to move things and making sounds. The cause is mostly trauma or strain and happens by young children of three years old or by persons in the age of forty. Some persons who are causing poltergeist activities are schizophrenic. Another personality caused the paranormal activities. There is no scientific explanation of poltergeist activities.
Scientist believe that a part of the human brains contains the ability to use mental powers.
A small part of our brains, the pineal gland, is the main source. Their is no evidence for this conclusion. Their are tests done by assistence of paranormal persons like Uri Geller, Matthew Manning but there was never found any reason why they have mental powers. But their is still some people who believe that poltergeists are ghosts or other paranormal sources who are using people for poltergeists activities. Because of their less intelligence they cannot do much harm and it always be there for a short time.