i've had this sub in my truck for about two weeks now. today i just changed the positon of it. it used to be on the drivers side in the ext. part of my truck facing the passenger side. i just put it in the middle facing the ceiling. and as soon as i did that, i could hear a vibrating sound comming from the cone of the speaker. i don't think it's blown because it sounds perfect up until a certain volume. and you can only hear it if your head is like directly above the sub.