The sound of soba is a result of the consumption. It is a sound you yourself emit when enjoying the carefully prepared noodles. Many know to eat the noodles with a sucking motion, rather than chomping down on the noodles mid way, but what is a more accurate description is a “slurp”, which creates a distinct noise. This is the sound of enjoyment.
Slurping the soba noodles is a skill that takes time and practice believe it or not. Begin by keeping your mouth close to your bowl of soup, or cup of sauce, and bring an amount of noodles to your mouth. The noodles you have in your chopsticks need to be bitten or “grasped” with your teeth to then be slurped, similar to a “vacuum” motion down the back of your throat for quick and smooth consumption. You don’t need to chew the noodles much.
There are a few reasons this slurping motion is key to enjoying soba. In the case of hot soba soup, it needs to be eaten quickly so as not to let the noodles go soggy in the hot soup. The noodles need to be slurped down and bitten in half as little as possible; this prevents you from ending up with a heap of noodle shreds and short pieces toward the end of your meal. Also, the slurping style of eating allows the full flavor of the soup or sauce to enter and coat your mouth. Lastly, the sound can actually be a way to acknowledge the cook that you are enjoying your meal; a very polite gesture in fact!
For me, the best way to conceive of the proper slurping technique is like when you are eating a very hot slice of pizza. You take a small bite, and because it’s hot, you start to suck in air while chewing. This allows you to eat the food while it is still very hot, while you are breathing in. This is the same manner in which you should eat soba in Japan.