I usually find that those strange noises in the night are coming from the ice maker on the refrigerator.

But it's the daytime noises that really bug me.
I was "home alone" one time then I heard a loud -- very loud -- tapping noise coming from the back bedroom. So I went in there and stood around a while. Nothing. Then halfway down the hall, it happened again. It was like a machine gun. It took me an hour to pin it down and it was a big woodpecker pounding on a downspout pipe just outside of the bedroom window. I have no idea what that bird brain was doing, but he surely wasn't going to get anything to eat out of a metal pipe.

Worse yet is the "someone-coming-in-the-door" noise. My computer is down here in our basement den. The kitchen door is right above where I am sitting, and just outside is the carport. This never happens when there is anyone else at home or when I am in any other part of the house, but I hear sounds like a car on the carport. Sometimes I even hear the parking brake come on. Then I hear the door open and footsteps directly over head. A few times, I have heard voices. So I get up to go see who is there and the place is empty. No car, door still closed, no feet. There is nobody there. This has happened dozens of time in the last few years and I have no explanation. The nearest neighbor is 150 feet away, we don't have a dog or cat, we live on a dead end road with little traffic. Maybe something is rattling around in my brain.
Howard