D'oh. Two and two together.

Following the Doctor Who speculation in the last post: so, Amy Pond's house appears to have an extra story. An extra story with stairs that look an awful lot like the ones in The Lodger. What happened whenever the timeship in The Lodger activated? The TARDIS went all screwy. Where was the TARDIS when it exploded? Amy Pond's backyard.

Um. I think I might've found what blew up the TARDIS. As usual, it was in the room (or, in this case, the house) with you all along.

None of which explains the who, why, or how, but at least it takes care of the what and the where.