There is no human tech that could do what the objects in the Nimitz sightings do unless you believe Area 51 has cracked anti-gravity propulsion or something similar.Like others above I would guess that government experimental tech accounts for most sightings.
I suppose that's possible and it is what Occam's Razor would suggest - it is some advanced human technology. But if it is human technology then we already possess the means to go easily to Mars and beyond.
I don't think aliens would come from outside the solar system to f*** with us like this. It's just too far to come and play practical jokes.
My personal belief is we are unknowingly sharing this planet with a non-human advanced intelligent species that originated either on Earth or somewhere in our solar system.