[Warren]

I think that if you used regular paper it would definitely rattle like that because there isn't much of anywhere for the air to go, it wont really go through the paper so it has to move the paper to get out and in. in concern to the cloth, As MiketheDruid said it could be because you didn't glue the entire cloth on to the backboard, you just glued the edges giving the cloth lots of places to vibrate against the backing. It should be glued entirely onto the backboard not just on the edges... makes sense and its worth a try to see.