The ratchet is perhaps one of the oldest instruments known, going at least back to the ancient Hebrews, and possibly further. It's a simple mechanism really; a gear assembly and a stiff piece of wood that rotates. As it rotates the wood slaps down on the next groove of the gear, making a harsh, flat noise. If you swing it quickly, then the ratchet, also called a noisemaker, will make a faster, machine gun rattling noise. This is the un-musical sound it's most known for, and it's used everywhere from holidays to football games, and everything in between.
Despite the image of the ratchet as a toy though, it's been used as a genuine instrument. Placed firmly in the percussion section, it's not something that you see much of in the classical scene, or hear too much of in opera. However there are musical styles, such as those that are heavy on the use of synthetic melodies, that love the noise produced by a ratchet. For heavier, industrial tunes the steady sound of a metal ratchet (the sort used as a tool in factories and other locales) is also a popular choice for a back beat.
The ratchet has, due to its instantly recognizable sounds, become a standby noise in other productions as well. For instance, it has been used in movies as well as in radio productions because people will know instantly what it is. Or, especially for radio, if the tempo is changed then the sound generated by a ratchet can easily be changed to sound like something else.
If you want to show your love for the ratchet, then you can find it emblazoned on a wide variety of clothing. Crewneck Sweatshirts are a primary example, and with the proper image it easily becomes a ratchet sweatshirt.