"(hasn't anyone told them that it's supposed to be in the background?)"

I think they've decided to treat the Dalek episodes as opera. And to be fair, at the points where the music swells, the details of the dialog aren't significant. It's a stylistic way of saying "...and at this point, everybody's just yelling at everyone else out of force of habit (daleks) or because they don't know what else to do (humans)."