There are studies linking reduced academic performance to noise pollution (in one, students in classrooms that were subjected to noise from nearby elevated rails performed more poorly than students on the other side of the same building).

As far as mental health effects: the difference between normal ambient city noises and persistent, intrusive, and/or unpredictable noises can be dramatic—take it from someone who spent a year working nights and then coming home to all-day construction about thirty feet from my bedroom...