Well yeah many people and companies develop flying vehicles, and lots of them have a similar shape. Heres the image of one:
http://www.autounleashed.com/images/moller_m200g_flying_car.jpgThat model of "flying car" is only sold in auctions right now apparently but yeah, it shows that it could be something similar. Notice how the propellers are not jutting out from the surface, and are probably invisible. It could have been something similar to this. Those move around very slowly, but this could have been some sort of military model of it that moves faster and flies higher. Could you assess its size at all? Also are you sure that it really ever broke the sound barrier or moved that fast? These machines can probably make an infernal sound when they start up, and the models youve seen might just make a sound thats so loud it sounds like a sound barrier break at startup. And maybe that what you thought was a super fast movement was really two of these vehicles blinking their lights and alternating, giving you the impression it was one vehicle being at one place and then the other.
Also, fishy thing though, if they was over you all the time and came only close enough that they were the size of a lemon in the sky, it means it never really went at your eye level or even close, so how could you see them from the side so you could draw that little pic with the glass window? This is making me think youre bullshittin' us....
I don't think that the military or private companies having and testing secret hi-tech vehicles or spacecraft is such an outlandish crazy idea in itself, I mean if a company indeed was working on technology that is so advanced it looks like its from outer space, they would probably want to keep it secret until they can find a way to market or otherwise use it, they don't want a competitor to just snag the idea or technology from them.
The only part that seems out of place or strange in this, is the fact you saw it. Why would they risk putting their big project out to be seen by people? Especially in this day and age when every other guy has a camera integrated to their cellphones. This didn't apply as much at all four years ago, but even back then it would have been a pretty risky thing to do. They would instead test things like that at large over the ocean or something.
Another possibility is that it really wasn't nearly as crazy as you remember it to be, and over time your memory beautified or crazyfied the image. From that point it could have been anything, from teleguided toys to simply a dream that marked you so much that over time you remembered it as something that really happened.
Heh it could be aliens too (no its not)