This is about the one letter to the editor and the Federal Aviation Administration rules covering altitude. The U.S. military doesn’t have to have the approval of the FAA for the low-altitude fly-overs. But they do coordinate with the FAA about routes and altitude for these missions.
One of the reasons they do these over towns and cities is to get practice for the personnel flying mock missions. They will have their mission assignments for practice for the real missions that they will someday have to fly when needed.
For instance, if they will be on a mission in another country which includes towns and or cities they will be used to flying low — and yes sometimes very loud — unless they use the muffled engines which some helicopters have, to quietly come in and do their mission with the knowledge that they can handle that situation.