Farts can make sounds such as pfft, squeak sounds or even be silent.
Also a fart can sound like the sound you make by pressing your lips together outwards and blowing it to make the raspberry sound.
Sometimes farts are silent as well.
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.
You would have to be really close to hear the movement of the muscles in your butt.
As a rule of thumb, the wetter the fart, the quieter it will be.
If it is really dry, it will be more like an air horn than a standard fart
If it is wet, however, it will be very quiet, although you will smell it for quite some time.
If you ever sat on a whoopi cushion the sound of a fart is really similar.