Noise is defined as unwanted sound. And we encounter it almost every day, no matter where we live. Cars and taxis honking on city streets. Jet planes taking off from the nation’s runways. Tractors and combines on farms. Air conditioners, generators, factories. Of course, people have varied reactions to the sounds they hear. What’s annoying to one person might be barely noticeable to another. But a growing body of research shows we have reason to be concerned. Excessive noise is putting millions of Americans at risk, not just for hearing loss but for heart attacks and strokes. For this month’s Environmental Outlook, a discussion on the dangers of noise pollution.