Can anyone describe how the almost circular rubber disc should be installed? The disc is about 26cm X 29cm diameter (10" X 11") and has had adhesive on one surface. I'm having the rear parcel shelf and blanking cover recovered but am not sure how this rubber disc should be installed. This is standard sound system and no extra sub/speaker fitted. I'm assuming the rubber disc is to provide sound proofing at that location. My best guess is that it should be glued to to the underside of the Blanking Cover.