At approximately 4:15 pm AZ time, my wife and I were interrupted in conversation by an enormous thundering sound. I walked outside and looked to the sky for what I though would surely be a low flying, large aircraft. Our local air traffic consists of small commuter planes, helicopters and very rarely, private jets - Otherwise, we frequently only see full sized military craft and commercial airliners at 20,000+ altitude. This sound was very deep and not exactly like a series of jet engines. There is a detectable "whine" accompanying most aircraft passing over, even from high up. This was an intense rumble that was more like close thunder that lasted continuously for 3 or 4 minutes. Looking to the sky, hearing this sound was really intense. It sounded more natural because of its intensity, than artificial. I have never been in an Earthquake but this sound is what I imagine an earthquake to sound like and fits the descriptions of how I've heard them described. We did not feel the ground shake or move at all. After scouring the skies above and looking around the streets, this rumble was clearly not a visible aircraft and it was not a biker gang rolling through town. As silly as that may sound, LHC is home to huge groups of motorcycle enthusiasts that regularly ride in large packs. A sound I am very familiar with. This unique rumble yesterday was unlike anything I've ever heard. I've Googled it and have not seen any other posting form anyone in the area. That's really too bad. I know hundreds of other people must have been in tune to it.