What kind of paranormal explanation is there for my couch shaking?

First off, make sure the couch is level on it's feet,and the couch structure is solid. Look to see the floor is securely attached to the joists and floor isn't warped. Notice,if any,natural phenomenom that might be causing shake(proximity to railways,heavy industrial traffic,seismic activity?). If not, then it could be some type of poltergeist activity is happening. Eliminating whatever natural causes that could contribute to situation narrows down the possible explanations as to why. Poltergeists seem to have a rather strong physical connective to our reality,hence;door knobs turning,objects thrown around,the typical stuff. Be cautious,if this situation starts to become more intense and uncomfortable,DEFINITELY contact an outfit that can assist you and arrive at a conclusion. Don't provoke it and don't be afraid,just be determined to be rid of it if you don't like what's happening.