Noise can actually be a form of pollution that characterizes urban and industrial areas. It affects not only the human hearing, but all our functions. The unit for measuring how loud a sound is, is called decibel. One decibel describes the minimum difference between two sounds, so that they are audible by humans. Whispering has an intensity of 20 decibel, while the sound produced by an aeroplane taking off, intensity of 150 decibel.
Noise pollution refers to annoying and even harmful levels of noise. Indeed, listening to sounds louder than 85 decibel for a long time can cause long-term deafening. Intense sounds also influence our mental health. They make people more aggressive and stressful. In addition to this, concentration is impeded and thus we fail to make the right decisions. At the same time, blood pressure rises and gastric juices' secretion increases. Those two processes can lead to ulcer.
The factors that cause noise pollution are pretty much known, heavy traffic, machines, extremely loud music, explosions and shooting (weather in reality or movies). It is a problem easily overlooked as something of no importance, especially when compared to other kinds of pollution that directly harms the environment. However, it is the kind of pollution that affects humans more than any other species, and thus we have to control it. Decentralisation of authorities and services (such as pharmacies, banks, schools) will make people prefer alternative areas of living, away from towns and noise pollution. That is a good way of tackling other problems as well, like the greenhouse effect in cities.