# eli5 – How are those random creaking and clicking noises of a house made?

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I lie in bed drifting of to sleep but I hear random clicking and creaking noises coming from somewhere in the house.

What is actually producing those noises? I’m aware with heat and cooling, joins expand and retract but to produce a quick clicking noise, I would expect it would require some velocity between two objects colliding. How are these noises made when nothing of significant scale is moving?

In: Physics

As joint cools or warms you are right the materials expand and contract at different rates. However friction between materials resists the movement so its not smooth and gradual. Instead once enough force has built up to overcome the friction…..then it moves suddenly. Hence the clicking type of noise.

The creaks are likely due to contraction of timbers etc when it gets cooler at night.

But I want to mention something else which may or may not be the case for you; it is for me. When you hear the clicks (not cracks), do they startle you, and make your heart rate race for a couple of seconds? This used to happen to me all the time, as I was just drifting off to sleep, I’d hear a big crack, which I always thought was TV discharging static or something, I’d get a flash of light behind eyes, it’d startle me and raise heart rate. Happens for years. Turned out it is called a sleep start, and more specifically in my case, exploding head syndrome (seriously!). It’s actually really common, and the reason I mention it is only as you asked about it when you are in bed and drifting to sleep.

Put your hand on a flat, smooth surface, applying a light pressure. Then, very slowly, try to drag your had across the surface.

For a split moment, your hand will have moved, but the skin contacting the surface will not have moved. You should feel this as a light tugging feeling on the skin of your palm. Your skin is building up potential energy like a tiny spring.

Then, all at once, the friction between your skin and the surface gives way and your skin snaps back to meet your hand. The energy of the “spring” has been released all at once. If done correctly this might make a very quiet sound.

Basically, all of the rigid components of your house are doing this constantly. The expanding and contracting cause them to slide past one another at joints, but just like your hand, the initial friction prevents them from moving right away. Instead, they build up energy like tiny springs, until they’ve built up enough to overcome the friction. The sudden “snap” is audible as a cracking noise.

The actual amount of movement is tiny. Imperceptibly tiny. But it’s definitely happening.

Part of why they seem so loud is that the big, flat walls of your home act like the body of a guitar or the shell of a drum, carrying the vibrations from the source and helping them get transmitted to the air, making them far more audible. If your house was just framework with no finished walls you probably wouldn’t hear much anything.