Also from what I can tell, this activity is far worse for some people than for others, it would be interesting to see scientific results of this phenomena being investigated, emf and so on, but the only defense I have seen is Jesus Christ of Nazareth, prayer, fasting, and praising God.
Hope this helps, I would be very interested to hear more about these experiences, it has been difficult finding a large number of cases to study, though it is obvious that this activity is widespread. Doors and windows seem to be the two biggest targets, one victim going as far as referring to people on yahoo! chat as "windowknockers", this person was assuming that other humans were physically causing this phenomena.