Several years ago I used to babysit for a wealthy couple who had two little girls. They lived in the "country club" area, high on a mountain. The house was (and still is, as far as I know) one of the biggest and finest in town, and people used to come driving up the mountain just to gawk at it. This couple had had the house specially built and moved in only about a year before this happened. As far as I know, there is nothing 'special' about the place were it was built - no old burial grounds or cemeteries, no strange happenings or violent deaths nearby.
One night (this was about 7 years ago now) while I was there with the children, the oldest girl (6) and I were sitting on the sofa watching a movie. The younger girl (3) had been sound asleep upstairs in her room for a couple of hours already. As we sat there watching TV I started to feel a little 'strange', imagining that someone was looking in at us through the windows. I wasn't really unnerved at that point, because I often felt 'exposed' in that room (a huge formal living room with whole walls full of glass doors and windows) after dark. Not wanting to frighten the little girl, I got up and wandered around the room, looking out at the windows to be sure no one was there - I saw nothing, and didn't really expect to. Then, as I made my way into the brightly lit entrance hall to check the windows there, I heard the very loud and unmistakable sound of glass shattering. I knew at once that it wasn't a window. This was the sound of some heavy glass thing shattering against a tile or marble floor (I was standing on a marble floor when I heard this sound). There was no doubt that the sound came from inside the house, and I was fairly sure that it came from upstairs. I wasn't imagining it, because the little girl heard it too, and ran to me in fright. I knew that the only windows an intruder could easily come through were those in the room we were already in (the house had 3 floors, one underground, and the land fell away from the ground floor in back), and there was surely no one there... the sound hadn't come from that direction. It still frightened me... I really couldn't explain why I had such an eerie feeling about it, but I did.
Not wanting to alarm the little girl more than she was already, I told her that something had fallen and broken upstairs, and we'd better go find it so that no one would cut themselves (what I really wanted was to check on the littlest girl, and to keep us all together).
The youngest girl was still sound asleep, and nothing had been disturbed in her room (which was thickly carpeted anyway, and couldn't have produced such a sound). With the oldest girl right behind me, I spent the next hour or so checking everywhere, upstairs and down, looking for anything that could possibly have been broken. I looked at all windows, even looked in closets, china cabinets and drawers to be sure. We were able to find NOTHING broken in that house, and I know neither of us imagined it because the sound scared us both out of our skins. Though I had tried to keep it lighthearted and not frighten the poor little girl, she seemed to have as bad a feeling about it as I did. Naturally she was not thrilled about going to bed that night, so I let her go to sleep there on the sofa next to me until her parents came home. I still feared that maybe something HAD broken, and I'd missed it... and if it can be found, you know a young child will find it and hurt themselves with it. With this in mind, I took the parents aside before I left and explained to them what had happened. They both told me that nothing of the kind had happened before, but the man assured me that he would again check the whole house completely in the morning to be sure there was no glass lying around. I called the next evening, and he had found nothing either.
That was puzzling enough, but a few months later the exact same thing happened again - only this time, thankfully, it was very late and the oldest girl wasn't awake to be frightened by it. Again I checked the whole house from top to bottom, this time with my mother on the phone as I went (Yes, at 29 years old - I was pretty scared!)... again I found nothing. I told the parents about it, just to be safe, when they came home, but they never found anything either. Nothing like that ever happened again while I was there, and if it happened to them, they never mentioned it to me.
About 3 years later they moved across town... but as far as I know, it had nothing to do with this incident.