You mention a housemate, apparently your sister. What's more likely: ghosts, hand-wavy stuff about electric fields, or your sister? Well, you know your sister, I know nothing about her.

Whatever the probabilities, the scariest hypothesis is that it's your sister doing all this. Poltergeists, whatever they are, seem to just do random weird annoying stuff. People, on the other hand, have purposes; crazy people can have crazy purposes.