perhaps you needed to turn down the gain and impedance settings on the amp and as a result of it, has send the woofer to overplay itself and the glue from the back of the woofer has come away from the cone. Try a continuity test with a volt meter from the woofer box terminals to see if you get a complete circuit. If you get NO reading, then you have a fault with the speaker itself! if you do get a closed circuit reading, play ur music and apply a little bit of pressure with your hand on the centre of the woofer pushin it in to see if the speaker cuts in n out or if u hear a crackling sound!? if u get nuthin at all...but u get continuity, it could b an amp problem. check the speaker wires connecting the amp to the woofer box.
Otherwise it may just be that the subwoofer has blown! Sometimes giving a new woofer a bit of power from contant music doesnt allow for it to break in eficiently and can potentially damage it even if you thinkit is new and should have lasted longer! I know I have certainly experienced that!