To squawk is to make a harsh screech, like the sound that a large bird might make. Your pet parrot might squawk until you give her treats to nibble on.
The imitative word squawk first appeared in the 1800s, and around 1945, the term squawk box began to be used informally to mean "intercom or loudspeaker." Today, that term is primarily used by investors and brokers to mean "an intercom used to communicate stock deals." In addition to being the sound of an irritated bird, a squawk is also a complaint: "All he does is squawk about how hard his new job is."