What is the actual cause of the continuous thunderous roar inside the 777, compared to the A330, or indeed even the 747 ? The racket is even more noticeable in the rear cabins. Is it the aircon, the way the engines are mounted, or what ? It is most noticeable, of course, if you take a flight on a carrier, eg Cathay, where you connect from one type to the other, so the difference is immediately apparent. It's a constant thing - Airbus used to refer to it some years ago in their advertising.