The US armed forces are working on making ships, planes and tanks "invisible".
Computers electrically "paint" the ship, plane, tank so that it disappears, or become indistinguishable from the background. Ships and planes are the easiest to to do this too since their background enviroment are the realatively simple sea and sky. Tanks will be much harder.
Sounds like USAF was conducting a test and got busted.
The interesting thing from your post to me is the noise. I attended my first airshow two years ago and I have to admit that the noise from those planes scared the hell out of me! The weird thing was that you wouldn't really hear it until they were right on you and then ZOOM!!!!! You wanted to duck even though they were hundreds of feet above the ground.
Although, I guess that if a plane is invisible then really it can make all the noise it wants really.