Have you ever stayed up too late trying to get to sleep? Tossing and turning to find a comfortable position to rest in, but you can't? Whatever reason it may be; legs are getting too warm, pillow is getting too warm, not enough blanket on one part etc.
Alone, in the darkness of your own room at night. Now, here, this is your own little sanctuary in the day; you know where everything is. Everything from your collection of video games and movies, to your laptop riddled with more videos and images of the latest Girls Gone Wild parties. Its an entirely different room when no light can or will enter.
What I am trying to get at are those quick and sudden pops and cracks you hear when the room gets too quiet. Ever hear those? Of course you have. They could be frequent... Pop... Pop... snap-pop... Or they could just be dormant for most of the night; maybe a single snap.
Most of us would simply brush it off because its such a frequent phenomena. It happens so often, so why should you care? Most of us probably find some way to explain it to comfort ourselves. Well, the heater is on, and it flows through the vents, and metal expands when it is heated, so that's what those pops are.
Its such a small, casual thing. A casual noise. No one thinks of it all that much. No one bothers to pursue it all that much. Such a little noise with such a little value.
Let's face it, though. Regardless of how you think of it, you follow them. Every little pop seems to be coming from another spot in the room. YOUR room. You follow not with your eyes, but with your head.
Pop... turn left... pop... slightly right... pop... straight up. You can follow with your head, but can you follow the noise to find out where its source is? Wouldn't it be the strangest thing if these pops weren't coming from the vent? If they had another source? But, what could they be?
Here's an odd question: what kind of flooring do you have? Hardwood? Carpet? Walk on the flooring, and you get a noise. Hardwood will creak loudly, while carpet will creak a bit fainter. Take this into consideration when you hear these noises while you sleep. It may not be, say, a heater, like you think it is. There is little to no distinction between making the floor react to footsteps, and the pops and snaps you hear at night in your room.