okay so i tried this just now, spent about 10-20 mins trying to tweak with it. Couldn't find and foam in the garage
so i used paper towels like kplax35. It kinda helped, but as i kept listening to music, it seems as the vibration from the bass and sub moved the paper towels around and the rattlign came back
looks like ill have to get some foam and try it.
Also CAUTION, dont be like me, use protection on fingers like gloves or something, i got a small cut from reaching into the holes :P