Examples of external noises are anything outside of a person's body that creates noise; a radio, a car, other people speaking and the hum of fluorescent lighting are all external noises. External noises are a type of distraction.
Unlike internal noise, external noises are difficult or impossible to control. When an airplane passes overhead and drowns out all other noise, there is nothing that can be done about it. External noises are all around. They overwhelm many with their capacity to distract. The more a noise is capable of distracting, the more it is considered an external noise.
External noise may seem like an invention of modern society, but even nature has an excess of external noise. The droning buzz of insects is one of the most common sounds, whether in a forest or city. The external noise of a waterfall is capable of drowning out all but the loudest voices. Even the weather can cause enough external noise to make it hard to think.
Every sound that exists outside of the mind is considered external noise. These sounds are capable of distracting and making work difficult to do. Even pleasant sounds like a favorite radio song are considered a type of external noise.