Daytime, low flying object

Girlfriend and I were sitting on the deck, i was watching hawks in the sky to just above but to the south. In the background i saw an object appear from above the trees to the west, flying between 300-400 feet, about 300 yards to the south. I pointed it out to my girlfriend, who confirmed what i saw. It was mostly grey, with some black on top. It was about the size and sort of the shape of a subaru outback, without the whole front, hood and everything, maybe a bit wider. It was completely silent, had no wings, no props. It held an extremely steady flight, no wavering, very consistent.. it flew to the east, maintaining speed and altitude, eventually we couldn't see it anymore.