Help!! might it be a ghost!!?

There are a dozen different explanations for this, including everything from routine noises of a house and wind to a friend playing a joke on you. A doubt a ghost, if such a thing exists, would spend its time running up and down your steps and whistling just to freak you out, it probably has better things to do. And if it IS the kind of ghost to do those things, it probably isn't going to start doing anything to hurt you, so I wouldn't worry. :)