After nearly fifteen years of running this website, I thought I'd received every possible question imaginable. However, a Peace Corps volunteer recently wrote to ask which countries are the world's noisiest. (Apparently the country that this volunteer is stationed in seems especially noisy.) I was gobsmacked! How could I never have received nor thought about this question before?!
Statistics on average national noise do not seem to be readily available. There have been recent studies which discuss the health and psychological impacts of noise. One report, Burden of disease from environmental noise - Quantification of healthy life years lost in Europe published by the World Health Organization last year reports gravely, "at least one million healthy life years are lost every year from traffic-related noise in the western part of Europe." However, that report doesn't tell us whether European countries are noisier than countries in Latin America, Asia, or anywhere else in the world. I did locate one article that claims Spain is the noisiest country in the European Union. Another source claims that Spain is second in the world with Japan as number one.
Then, I found another article which claims that the United States is the noisiest country but in browsing the related report, I couldn't find evidence of an international study. Also, someone claims that within the U.S., San Francisco is the loudest city.
Due to the variability in measuring how "loud" a country is, I doubt we'll really be able to compare some place to another anytime soon. If you have thoughts on these matters, I'd love to hear them in the comments below...