Right so this is the kind of post I've been waiting to see on here. I had something similar happen about two years ago near a reservoir outside Leeds, it was just hovering totally silent and then gone in like half a second, no noise, no trail, nothing. Still can't explain it.
What shape was it roughly? And did it have any kind of light coming from it or was it more like a dark shape against the sky? I find the silent ones are the most unsettling honestly, a plane or drone you can usually hear before you even see it.
Have you been back to the lake since? I always think the location matters, like certain spots just seem to have repeat activity and water seems to come up a lot in these reports which is something I find really interesting. Would love to hear more details when you're ready to share them.