Electric drones could make small package deliveries cleaner. But in North Texas, Amazon’s Prime Air program faces a challenge: winning over people beneath the flight path.By Andrew LiuRICHARDSON, Texas—Jonathan Pace first noticed the noise. But it wasn’t until he bought a Bluetooth-based drone tracker that what seemed like a neighborhood nuisance became something he could measure: how often Amazon drones flew above his home—and how low they flew.