This video was recordered in October 2011 on the Apache trail in Arizona. The strange sound seemed to come from the sky and there were no airplanes there at the moment.
The author’s comments:
It was a beautiful, relaxing day on 3/10/2012 on the Apache Trail in Arizona, USA. We decided to get out of the car and look around the desert. The sky was crystal clear, however, we heard a strange sound coming from the sky. We didn’t see any airplanes or trails from them. No one was around either. Apache Trail is very close to Phoenix which is known for the, “Phoenix Lights” which were a group of UFOs seen in the 90’s.