Tim Mulligan moved to central Manhattan so he could be closer to work and avoid a daily ordeal on the rattling, screeching subway, just one part of the urban noisescape that tests New Yorkers every day.

"Even with your earbuds in, turned all the way up, you can't hear anything for the whole commute, and you're ruining your ears at that level," said Mulligan, a US Marines veteran who lives with PTSD.

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