This event happened at my parent's house when I was either 16 or 17.
My parent's house has always been 'strange', even to this day. Ever since my brother and I were small, I remember weird events happening every now and again. It was when I hit my teen years did the events become more 'creepy' and regular.
My brother had been working late shifts, well past everyone's bedtime. We only had one functioning car at the time and that car had always been parked outside. My brother didn't have a key to the back door so he would have to go through the backyard and tap my window to wake me up so I would get up and go unlock the back door.
I was out like a light one night when I was abruptly woken up by an awful tapping against the glass of the backdoor. It sounded like someone was hitting the glass with all their might with the tip of a key or something metal.
I woke up in a panic, thinking that I had missed my brother's initial window-knocking signal to wake up, and now he was angry for being left outside. As I scrambled out of bed and ran through the dark house, it did not occur to me that the noise was so very loud and the tapping absolutely did not stop, pause, or hesitate at all. It was a constant tap tap tap tap tap, and honestly it would be loud enough to wake up everyone in the household. It truly was that loud.
The tapping continued even as I approached the backdoor. I flipped on the backyard's light and the very second that the light flooded the area and I looked out the glass panels to see no one there, the noise stopped. Dead silence. I was all alone.
Confused, and hoping that my brother was playing a trick on me, I went into the living room and peeked out the curtains to see if his car was there. Nothing.
At that point I got very, very creeped out and turned on the family room lamp and watched TV until I saw my brother pull up to the house. I didn't want to sleep until the sun rose.
The next day I did ask my parents if they had heard anything the previous night. They said no, but I find that impossible since they always leave their small bathroom window open and it is 10ft or so away from the back door. They aren't the heaviest of sleepers, either. No one in my family can reason this event away, so whenever it is brought up we always get goosebumps!
Thankfully this did not happen again.