Hauntings come in many forms, there are poltergiest activity, sounds, voices, touches, and even full visuals. They can be brought on by many things be it bones, energy left in an object or place, even can be attracted by a person.
One of my favorite stories took place in North Carolina, a young man of 20 was living at home with his mother but for months had been suffering visions of civil war soldiers walking thru his room. The feeling of being held down overtook him each time he slept in the room.
As it turned out his home was built on the site of a massacre that had taken place in the civil war where several 20 yr old men had been killed in thier sleep pinned down by bayonettes to thier beds.
In an attempt to rid himself of these problems the young man finally moved out and has not had any activity since.