Until Monday, I had not flown on a 777 in years, I've been mostly flying on 747s, A330s, A340s and of course the boring 737s and A320s.
When I did long ago, I also remember seating further back on the plane; Monday night I sat on row 21 of a United bird; as soon as I took my seat, I noticed the plane was really loud, I could hear what sounded like an engine or generator under my feet, kind of uncomfortable by the way.
Other topics mention electrical noise, until they start the engine, however, this sound lasted until after we were past 5,000 ft per the flight map, then, when we were approaching our destination, the "engine" came back on, was still on when I deplaned and I'm assuming it remained on until it departed back to the US.
Can anyone clarify if there's an engine/pump/generator on that area of the plane? I'm sure this is a stupid question, but, I've never heard a similar sound before on any other plane, including other 777s; the worst part is that I've always been a Boeing fan, and after this, I would definitely take an A330 before a 777 (comparing apples to oranges, I know, but still).