While I was in the military (USAF), one of my tours overseas was spent at RAF Upper Heyford, near Oxford, England. In fact, with extensions and a second tour, I spent a total of 11 years there.
Anyway, during my first tour I decided to move into a house in New Marston, a suburb of Oxford, that I shared with three other people. It wasn't a very old house; in fact, it was fairly modern. Not long after moving in, I was in the home alone having a bath when I heard 2 taps on the bathroom door. I figured one of my house mates had returned and so I yelled "yeah!?", but there was no answer. After finishing my bath, I had a look around and found that no one else was in the house.
I never really gave the incident a second thought. Then, as I continued my stay there, I began to notice in my peripheral vision (the corner of my eye) some movement on the stairs to the bedrooms or sometimes while I'm walking around up stairs. In both cases, I would turn in that direction and there would be no one there. After experiencing this a few times, I began to realize that THIS HOUSE IS HAUNTED! Then I would think back on the episode that occurred while I was in the bath and come to the scary conclusion that an apparition was making itself known to me. Yikes!