I think I once had an experience with a haunted ghost.
I was 11 years old, and at home with my sister. Nobody else was at home. Anyways, I was playing outside when suddenly, for a moment, everything became silenced and isolated, and then I heard someone knocking on the window and then a girl yelling "Hello, Hello" at my grandma's house upstairs (closely neighboring our house). After this brief encounter, everything, the surroundings, birds etc. were at normal again. First I thought my sister was playing a prank on me, but soon after the spook she started playing piano from our house, so she couldn't be up there in my grandma's house. Hell, I couldn't explain it.... But my grandma's house is very old, and allegedly a girl once died in it some 60 years ago.