It's not just the United 777s, it's ALL 777s that are loud inside, especially in the rear cabin. Now I know that airline execs and senior designers rarely travel back there, but if they did (especially on overnight flights) they could be in for a surprise.
In contrast the A330/340 are notably quieter at the same relative position. Anyone got a technical explanation for this ? More soundproofing ? Engines mounted further outboard ?