Just moved into a new house and some Polk wall speakers are mounted on the wall. I can't figure out how to remove them. They look like they were large surrounds. They are an odd shape with seperate tweeter and mid and the enclosure has 2 plastic discs on the rear that seem to be some kind of axle for mounting. A sticker on the discs says point arrow towards rear (or something like that). I've pushed, pulled and pryed, but can't seem to get them off. Anybody know the trick?