Why do soda cans make noise when empty?

Blowing across the top of an open, empty bottle or soda can produces a typical sound, formed when pressure waves are excited at a characteristic frequency. For an empty soda can, this so-called Helmholtz frequency is 420 Hz — just below that of a concert A.

Why does a soda can make noise?

Coke is bottled under pressure to ensure that the proper levels of carbonation are present when the drink is opened. When you open the bottle the excess gas rushes out of the bottle and a hissing sound is heard. The dissolved gas then slowly bubbles out of the drink.