Some reported poltergeist activities has been known to cause pianos to play random tones. But only occurred when the teen-aged daughter was home.
If you were to look up the meaning of the word poltergeist in any paranormal glossary, you would find that the term in German means a noisy spirit. I never understood why that meaning was given to the word because, a poltergeist is not really a spirit or a haunting at all, even though it is considered to be paranormal.
Poltergeist activity is usually brought on by a persons ones own mind, caused under stress of some sort such as fear, anger, or, a strong feeling of helplessness. Not every person will have the experience. As a matter of fact, it happens to very few people. Although, for a person who does indeed have these experiences, they usually have them more then once in their life time. A poltergeist experience can make light bulbs explode, noisy knocking sounds, make electrical equipment malfunction and, make objects move or levitate without anyone being near the object.
I went all through Jr. and Sr. high school with a girl who when she became very stressed out, has actually made every light bulb in the room she was in burst and, also, made the radio beside her bed come on.
That sort of experience is very real for some people. The bad part of that is, people who do have a poltergeist experience, have no control over it. It happens when it happens and cannot be controlled and happens to female teenagers more so then to males. It has been debated though if the poltergeist phenomena is because of spirits harnessing the energy from emotionally teens or if the teens themselves have telekinetic abilities without knowing about it.
For instance this happened a few times to my mom, as described in When Your Energy Make Objects Fall and sometimes the cause is of someone in emotional stress as in this entry called Telekinesis and Poltergeist Activity. More about how the poltergeist phenomena might work is explained in the entry about Electromagnetic psychokinesis.