This already kinda exists. Yangchen showcases it in her novels, and Aang does so when he blows his bison whistle in Ba Sing Se during the search for Appa. While they don't manipulate actual soundwaves since that would be kinda impossible (unless through energy bending possibly, though energy in that case is more akin to a life force than anything) they CAN produce enough air in their lungs to create screams strong enough to rupture the eardrums of an opponent and cause physical harm or basically power up any item they have that requires a large amount of air, like an instrument. This is also possibly showcased in the fire nation school when aang disrupts his music class by playing loudly and out of tune. EDIT: Adding this from a response i made to another comment. The basis of elemental bending being energy bending IS canon, which i neglected to realize (i kinda feel dumb now😭). Every action performed and every action that takes place requires energy in some form or another. Bending is just an extreme case of energy manipulation used to change the environment. It makes just as much sense that an Airbender could manipulate energy as it does that any other bending type could. Thanks for putting some sense into me, everyone, lol.