Treeline hovers are the ones that stick with you, trust me. Had something similar over the woods behind Farley Mount about three years back, dead silent, no navigation lights, just sitting there like it owned the place. The silence is always what gets me - aircraft make noise, helicopters make a racket, but these things? Nothing.
What colour was it? Any shape you could make out or just a light source? And crucially, did it move off suddenly or just sort of... fade? The exit behaviour tells you more than anything else in my experience.
Post any photos or video even if they're rubbish quality, someone here can usually pull something useful out of teh metadata or run it through some filters. Don't sit on it thinking it looks too blurry to bother, we've worked with worse.