Had something similar out on Dartmoor about two years back. Just this silent shape, low over the ground, no sound at all which was the part that got under my skin the most. You expect something mechanical to make noise.
The thing that sticks with me is how long it just... sat there. Not moving, not doing anything obvious. I had my recorder going for EVP work and when I listened back there was this low hum underneath everything, almost sub-bass, that I genuinely couldn't hear at the time.
Did you notice any sound at all, or was it completely silent? And roughly how long did it hover before it moved or disappeared? Those details matter more than people realise when you're trying to work out what you actually saw.
Would love to hear more about this one. The field location is interesting - a lot of the sightings I've read about happen near open farmland rather than built up areas.