Bone stock sound system and yes I dd this car backwards daily... I like the extreme. On a serious note: The "explosion" if you want to call it has an epicenter right at one of the heating lines.
What I noticed was an oval burn mark around that heating line that matched the epicenter. Also, it looks like someone took a knife and cut holes in that exact part of the heating line which is not possible as it is inside the glass. My friends and I think it may have been electrical.