As MAFFY said, that's merely an unfinished area that the player isn't supposed to be able to visit, nothing secretive. The voice clip was likely intended to be an audio trigger there (there's another partially implemented sound at the door to Mr. Burns' mansion). Also, this post appears to imply that the sound DOES play in game if the player goes behind that house? From what I recall, they don't play at all due to an incorrect file path in the level's RMS file.
EDIT: Checked, there is no trigger inside of the house.