As paranormal investigators say, 80 - 90% of their cases turn out to have explainable causes. And these causes have cures that you can do yourself. Bnd.com has written and posted a nice article on these common problems with some solutions.

-Mysteriously moving doors? It’s creepy to watch a door open or close on its own, the work of some unseen visitant. Relax. The door merely is maladjusted, or the house has settled. The simple fix: Remove a hinge pin, lay it on a concrete surface and give it a satisfying whack with a hammer to produce a slight bend in the pin. This creates resistance in the door’s swing. The more complicated fix involves tightening screws and hinges, maybe rehanging the door or resetting the frame, in which case you might want to consult a handyman, avoiding those who work only when the moon is full.

Sounds like solid advice.