Karthic thallikar first noticed the noise sometime in late 2014, back when he still enjoyed taking walks around his neighborhood.

He’d been living with his wife and two kids in the Brittany Heights subdivision in Chandler, Arizona, for two years by then, in a taupe two-story house that Thallikar had fallen in love with on his first visit. The double-height ceilings made it seem airy and expansive; there was a playground around the corner; and the neighbors were friendly, educated people who worked in auto finance or at Intel or at the local high school. Thallikar loved that he could stand in the driveway, look out past a hayfield…