A Poltergeist is a noisy spirit that is supposed to be able to move physical objects, and throw physical things. Poltergeists can manifest smells, including bad odors. A ghost might be more of a fine spirit that can be seen through. Poltergeists are negative spirit energy, and ghosts can be, too, or not if they choose not to be. Poltergeist is a German word, so Poltergeists must have a history that goes back a ways. There was a case I think in England, where Poltergeists were apparently throwing stones at some windows, that might be believable.