 I don't remember if it was an exterior wall or whatnot, but maybe try to see if there's any shifting or any movement that you can see. Because if there's any cracking up at the corners or up along the ceiling and things like that in the paint or the drywall, then you're definitely probably getting into a structural issue. My other thought... My next thought would be go underneath down in the basement, get into where you can see the joy space, and...