Hello again,
Thanks to all for replying to my original question. Perkin - definitely not flaps as we were high and still flying quickly, plus I did look outside and they weren't extended. The noise was very mechanical, I don't think it was airflow. Slim_slag mentioned fuel pumps, and I know the post was made in jest, but I did wonder if that's what it was although I'm quite confident we weren't running out of fuel
. I think on several aircraft the fuel is balanced before landing so maybe that's what it was, but I really don't know. Apaddyinuk (great name!) - that sounds utterly feasible although I have no idea what one of those packs sound like, and as I said, I've not heard the noise before. Then again, sounds can be different depending where you're sitting so that might explain it.
TightSlot, thanks for the offer. If you think it's worth it I don't mind the thread being moved, but it really is just a question from a curious passenger. If I'd been a bit more awake when we left the aircraft I might have thought of asking the crew. Oh well, too late now.