This happened in 1983 or '84. This was the summer time in Oklahoma. I was a college student at the University in Edmond Oklahoma which is a suburb on the northern side of Oklahoma City.
A friend of mine was trailer sitting for a friend of his who was on the road for a few weeks. He was a musician. When say trailer sitting I mean a mobile home. If you don't know what that is I'll try to describe one. It is an inexpensive prefabricated 'house' that can be moved by a large truck. They have pretty thin walls and are generally about 15 feet wide and 60 feet long. In the country they are popular because it is much easier and cheaper to just have one of these things hauled out to a piece of land than actually building a house.
This particular house was about 30 miles north of town and in a park with some other trailers. The other trailers were about 75 to 100 yards away. Each trailer had a street light over it but on a cloudy or moonless night it was pretty dark between houses. Now my friend asked me and my girlfriend to come out there for dinner because he was 'lonely' out there by himself (the little liar!). After dinner I was sitting on the couch which was against a wall of the trailer. I FELT a heavy thump against the wall from outside through the couch. Everybody heard it also. I thought that there must be someone outside hitting the trailer. However my friend quickly explained that this had been going for a few nights and he was glad he now had witnesses. We then experienced thumps on the side of the trailer and knocks on the door and no one there when you look out the window. Now because a trailer is basically a rectangle it wouldn't be difficult to hide by simply lying flat on the ground right next to the trailer. We thought that it was a person harassing us or wanting us to open the door so they could rush in. The next few nights I stayed there with my friend. Several things I noticed. The street lamp over our house would cut out from time to time. Possibly a short yes but its cutting out was always the prelude to the noises. Around the trailer was a ring of dirt that was about two to three feet wide where there was no grass. I raked the dirt into a simple pattern. The next day after many bangs...no tracks. While the thumping was going on we would blast the alarm for the house which made a loud siren outside. This did not deter the bangs and never awoke the neighbors. When the bangs were sounding nowhere near the door I went to the door (gun in hand) to go out an confront the person. However a terrible feeling of fear would overcome me at the door. I would shake and felt very ill and could not turn the handle. If I stepped away from the door my courage would return and I would start for the door again but would not be able to open the door. Finally after several nights we did go only to find nothing. My friend decided that his friends stuff did not need to be watched that closely and stopped going out there at night.