"Transformers hum, CRTs whine and sizzle, speakers buzz and hiss, and sometimes electricity arcs causing a popping sound as it interacts with the air" That is

"Transformers hum, CRTs whine and sizzle, speakers buzz and hiss, and sometimes electricity arcs causing a popping sound as it interacts with the air" That is what is interesting, and what I am interested in. What causes those sounds? They obviously aren't weird superstitions, so what is the rational explanation?