Noise can be bad for child development

Exposing children to cluttered noise for an extended period of time—even the background noise that comes with urban living—is enough to hamper their intellectual development.

Adam Alter, Drunk Tank Pink: And Other Unexpected Forces That Shape How We Think, Feel, and Behave (New York: Penguin, 2012), ch. 8 (citing S. Cohen, D. C. Glass & J. E. Singer, "Apartment Noise, Auditory Discrimination and Reading Ability," Journal of Experimental Social Psychology, vol. 9, pp. 407-33 (1973). (I haven't red the original study, but I wonder whether they controlled for lead pollution. The apartments on lower levels would have also been exposed to more lead in the atmosphere from traffic as well as more noise.)