Original poster here again. Someone mentioned the Chapel Hill Airport. I live < 1 mile from the airport and can hear planes (on occasion) taking off/landing at that airport. It doesn't get much traffic. It has medical flights fairly routinely. Then, on "game" days, there are assorted little jets coming and going.

My mystery plane is not using the Chapel Hill Airport...I know the sound of those planes. It's someplace above, I can hear it coming from the distance, then almost immediately above my house, and then I hear it going into the distance.

I'm glad that there are all these thoughts out there about what the plane is doing. At least now I can pick the favorite story and believe that's what the plane is doing. I think I'll choose Blackwater.