It sounded like a slow moving propeller, with humming noises and a louder static-electricity zapping sound.I got up early this morning around 2:00 a.m. to let the dog outside. I couldn't go back to sleep, I didn't even try. I was sitting at the computer about 15-20 minutes later when I heard something outside that I have never heard before. It sounded like a very slow moving propeller (almost what you would expect a boomerang in slow motion to sound like). There were other noises accompanied by the propeller sound one was a steady humming (vibrating) noise and the other was a static-electricity sound (like an electrical zapping sound) that was louder than the humming but not as loud as the propeller sound. The electrical zapping sound could be compared to a soft buzzing sound. The sound seemed to come from the northwest and moved off toward the northeast. After hearing the sound I scolded myself for not having gone outside to look. I realized though that the sound almost mesmerized me, and I didn't move the whole time I heard it. It sounded like it was right outside my window, directly above my house. It seemed to be hovering directly above for 30 seconds. Between the propeller sounds which were louder than the other sounds there was a 3-4 second gap which is how I heard the humming/vibrating noise and the occasional zaps/buzzes. I'm certain this was not a helicopter, or anything I've ever heard before.