Farts can make a lot of different noises. Some are high and squeaky, while others explode like a car backfiring—and some don’t make any noise at all. How loud a fart is depends on how much gas you have in your intestines and on the muscles around the anus.
Farts happen when your body lets out gases. Some of that gas comes from air that you swallow as you’re eating and breathing. Some of it is made as your body digests food to turn it into energy. Bacteria living in your gut help with digestion too. As they do, different gases get released. Those gases move along through your large intestine until they reach the rectum. Then they come out as farts: some quiet, some loud enough to rattle the windows.
The sound of your farts is affected by how much gas has built up inside, and how fast it comes out. It also depends on how tight the sphincter muscles are. They ring the anus and help keep it closed. All these things together cause vibrations as the gas pushes through. If the sphincter is relaxed, your fart will probably be on the quieter side—pffft! But if those muscles are tightened up (as they are when you are trying not to fart), you’re probably going to squeak, toot, rumble, or roar.
A version of this story ran in 2016; it has been updated for 2023.