yea, a couple of years ago i was the only one home so i was watching TV and all of a sudden it sounded like a bowling ball or something was dropped in the kitchen. scared the holy shit out of me even the dog jumped up barking. went to the the kitchen nada, nothing there nothing broken nothing out of place. went outside again nothing hit the house. got a ladder and check out my roof and still nothing. i dont have a clue on what the hell it was, but it was loud and violent, i thought for sure was going to find a hole in my kitchen floor.
There was a water-hammer issue here in the apartment awhile back. The convenience store in the other half of the building had a soft icecream machine, and every so often it caused some rapid pressure fluctuations, which made the pipe under the kitchen floor start pounding against it like crazy. Scared the hell out of me the first time it happened.
The more recent thing for me was a few days ago. Fairly quiet in the bedroom late at night, lights are out, and then it sounded like something very distinctly tapped the floor twice, about 2 seconds apart, just 2-3 feet from the head of the bed.
Really creepy to hear something like that.
I turned on the light only to find...absolutely nothing. Not even a mouse or an insect or anything.
The effect still hasn't really worn off on me. I figure that it was just the frame of the building re-settling due to the change in temperature, as I'd been away for several days, so it was the first time in about a week that the air conditioning was on. But Jesus...it wasn't easy sleeping that night.
The really fun part: The head of my bed is near to the closet, which is open to the crawlspace behind the wall. The cramped, dark, cobweb-ridden crawlspace. You could have quite a few people hidden back there.