This may sound like a bizarre question but it's been puzzling the hell out of me and I figure this is as good a place as any to try find an answer.
A few nights ago something flew over my house at around 2:30AM. I say something because I have absolutely no idea what it was. I didn't see anything, but the sound it produced was unlike any aircraft I've ever heard. It was much louder than anything I've heard come over at that time in the morning, and the only way I can describe the sound is that it was a low, loud, steady and intense hum (almost like a sine wave at around 80Hz if that's of any use). I've heard props make a kind of humming sound before but the character of the noise this aircraft produced was completely different. It sounded nothing like any turbofan I've ever heard. After probably around 30-40 seconds of the noise staying at the same intensity it faded slowly, much more gradually than when aircraft usually fly over. I was practicing bass guitar on headphones at the time and heard the noise at the end of a track, so I have no idea whether it came about gradually or quickly.
It was almost like a police helicopter came overhead, hovered for a while then went away at very slow speed. Living in Bradford I get to hear the Police helicopter on a fairly regular basis, and this sounded nothing even remotely like it.
Does anyone have the vaguest idea what this could have been? I live around 8 miles south-west of LBA if that has any relevance.
Any ideas anyone?