My friends and I were coming back from a camping trip on a sunny afternoon about 12 years ago. We were driving on an interstate near an air force base. We saw a C-130 ahead of us coming in perpendicular to the interstate, about to cross it apparently approaching for a landing at the AFB on the other side of the highway. As it was coming over the treetops in a pine plantation and just about to cross our lane, we all noticed that it seemed to be flying low and moving really slow. REALLY slow. It appeared to be only at most 100' over the tops of the red pines and moving at about 20 mph.
Thinking it might be having trouble, we slowed down the car and rolled down the windows to get a better look. We were surprised to hear that the plane was making absolutely no noise whatsoever. No engine noise, no "swoosh" of the air over the wings. Nothing. In the time it had taken us to drive the mile or two from where we first saw the plane, to where we were underneath it, the plane appeared to have travelled only about a quarter mile. Even though it was less than 100' from the tops of the trees (probably only 70' as it got to the edge closer to the interstate), no one branch or needle on any of those trees moved an inch. As we drove under its flight path, it was moving so slowly it appeared to be stationary. It was moving as though it was a C-130 shaped dirigible just wafting over the interstate!
My friends and I have talked about this incident many times and done some reading since it happened. C-130s have a lower limit of airspeed ( I forget the technical term) of somewhere around 100mph. This plane was doing less than a quarter of that. Any plane that size flying that close to tree tops should've caused considerable downdraft which would've caused nearby (directly underneath) trees to move quite a bit in the breeze. I imagine a C-130, at that height, overhead and approaching a landing, would have been making a lot of noise. Certainly more than NONE AT ALL! I used to live under the approach path of a regional airport. Planes flying at many, many times the altitude of this plane were plainly audible inside inside my house. This one made ABSOLUTELY NO NOISE WHATSOEVER!!! Even when we slowed down to ~40mph with our heads craned out the windows, we could plainly see it was just floating there. Just silently wafting over the busy interstate in broad daylight for everyone to see.
Weirder yet, several miles down the road, when we were past a large wooded area that obscured the AFB from the interstate, I saw what appeared to the be the same plane just hovering about 100' off the ground oriented about 180o from how it had been pointing when it crossed the highway.
My friends and I who saw this have talked about it several times since then and all recount the exact same occurrence, with some differences in values like speed and altitude (not everyone is exact). We all at some times or other try to look online to see if there're any explanations to what we all saw or maybe just some other witnesses. I still have no explanation, and I still get chills thinking about it.