What makes people notice our drones? The loud rotor sound. We, at a hobby level, can't reduce the rotors cutting through the air, sound. But, noise canceling technology has been 'out' for quite awhile now. It works best if you are wearing headphones. Here is how it works: Sound is a Sine wave as is our household current. Think of a straight line, with a line shaped like a perfectly round hill. Then, under the line, is an upside down hill, the same size and height of the right side up hill, then imagine that pattern continuing. You just learned what a sine wave is, somewhat! These noise canceling headphones use a microphone to 'listen' to the sound around the user. The electronic circuit, then produces another sine wave at the same height as the 'hills' in the other one, with one difference. The electronically produced sound is out of phase with the surrounding sound. Imagine the first sine wave, a straight line with an upright hill, an inverted hill, an upright hill, etc. This is the outside, of the headphone, sound or the ambient sound. Imagine another horizontal line below the first. This one has the same hill pattern, BUT when the ambient sound has an upright hill, or produced sounds to the headphones has an inverted hill. It is like adding -5 with +5. The result is 0. For sound waves, this means the ambient sound has been cancelled out by the generated sound, so you hear absolutely nothing! You could be operating a jackhammer and YOU would hear nothing. This isn't like putting in ear plugs, that reduces the sound. There is NO sound going to your ear drums! These headphones are used around loud equipment. They are also available with a built in radio or an audio input. Say you are in a subway car, you won't hear the sound of the car, nor the passengers talking. You will only hear your music or turn that off an you hear nothing. You could nap surrounded by jackhammers. But, if you wanted to do that, go to a doctor as something is very wrong with you! This is easy to do with headphones. It is harder to do with a speaker. This is just us brainstorming, but say you put a speaker and audio amplifier on your phantom. You produce sound at the same volume level and inverted from the rotor noise. There are many complications as people will be in different locations. But, I guarantee you that our military has worked out the bugs where their/our stealth helicopters make very little sound compared to without this technology. They do more than just that, they design the rotors for reduced sound. Maybe I'm nuts, but there is a very strong anti-drone movement. If the public can't hear our multi-rotors, they won't know to look up. Even if you don't understand how it works, what do you think about reducing your bird's noise? Any other thoughts on how to minimize the sound, besides height? Or, a way that we can see our bird, but others can't? I think that may be possible.