I imagine they'd have to be limited to vertical paths anywhere near the ground, otherwise as you say the noise of hundreds of drones would be unbearable. I don't see any reason why there shouldn't be a few stations around urban areas for silent landing/launching i.e. nets for drones to drop into(potentially assisted by small parachute/wings) and launchers(catapults etc.) to get them out of earshot before they fire up their motors. You'd still have a little activity in the last few meters but how many deliveries are actually delivered to a particular area per hour?