When I was about 13 or 14, a small farm in the village I lived in was sold. It was bought by a housing development firm, who proceeded to build a new house* on the land. They took the large, old farmhouse and started converting it into 3 separate dwellings.
As kids, we liked to play on the building site when the builders were off after school and at weekends. We would play in the houses, and up in the rafters and on the machinery.
On one specific occasion, four of us were playing in the old farmhouse. Some of the rooms upstairs had been completely stripped, and only had the main floor supports running across the rooms, and we were running across these beams, generally making a lot of noise as kids do. All of a sudden, there was a loud shout which seemed to come from the other end of the house, but from an unknown source. It was a shout as if by a security guard who wanted us off the property, this is who we thought it was initially.
We ran towards the ladder which ran from the first floor to the ground (as the stairs had been removed) and started looking for who had called out. We saw no one. Then a second shout rang out, from the direction we had just come from. This is when sheer panic set in, and we all couldn't get down the ladder fast enough.
I was the last down the ladder and as I was almost on the ground, I looked up. And to my total shock, I saw an old man looking at us with a very disgruntled expression. He was wearing a shirt and brown trousers and I would put him at mid - late 80's at a guess. There is no way he could move from one end of the house to the other undetected, and then to the ladder top in such a short space of time. And since then I have thought if he was on "patrol" he would have been wearing safety wear. Needless to say we ran, and then dared each other to go back, and once we finally did, we saw no one.
To this day I believe he was an old inhabitant of the house who was not happy with us playing there. The houses were converted, and people moved in. I got talking to one guy who lived in one of these properties in the local pub a good few years later, and after a few drinks and flowing conversation, I asked him if anything "strange" had happened in his house. Although he did not go into detail, he said he had experienced knocks and bangs and also footsteps on the odd occasion.
*word has been changed during editing (Griff, my apologies... The word was originally "close" but it didn't seem to be right.)