Poltergeist activity is thought by many researchers to be a product of our own minds, our own subconscious reacting to stress or some other factor that can result in the kind psychokinetic and audible phenomena you describe.
Haunting activity is something outside ourselves -- a residual haunting, which is like a recording of some past event (the footsteps and voices) on the environment (your house), or an intelligent haunting, which is an active spirit in your house.
In any case, it seems like an investigation might be in order to get to the bottom of what's going on. A good paranormal investigation group in your area should be able to consider your experiences, try to rule out any logical or mundane explanations, perform experiments and tests, and try to come up with a solution. They may set up equipment, such as audio and video recording gear, to see if they can document the phenomena that has been bothering you.
If it is poltergeist phenomena, it will probably fade and disappear after a short time. If it is some kind of haunting phenomena, the paranormal group may suggest a cleansing ritual of some kind to help get rid of the activity; this sometimes works.
Check around for that paranormal research group in your area, and be sure they are people you feel comfortable with and can trust.