I've seen the episode in question (and the youtube video that asks the same question you do).  IMO it seems that the whispering is probably the little girl who lives there (IMO it sounds like most of the EVPs were from her, but that's another discussion).  The little girl was wandering around in the background in the shots previous to this, and was being watched after by another adult… it sounds like she's just saying something to the other adult, but off-camera, possibly in another room.