here's the build log, there's a video in the last post on the first page, and another on the second page.
http://www.stevemeadedesigns.com/board/topic/134756-videos-the-mighty-mini-build-2001-silverado-z71-4xsa8s-apsm1500/page__fromsearch__1
what part of the box is flexing?
it really doesn't come across as being very loud in the video, are you sure the woofers are all in phase?