I'm not sure who's mouth it comes out of, thinking it might be like a director's mic still on or something?

In season 3, episode 3, titled Lobster, When Jenny and Moira return from their trip and Shane asks Moira if she wants help bringing her bags into the bedroom, Moira says "No thanks, I've got it", and then immediately after you hear someone whisper "f***ing b**ch". I wonder who says that, let alone why ...

****edited by another reviewer to clarify: What is whispered is "F***ing bedroom?!" and it is said by Carmen. You can see her saying it, as the words come out of her mouth.