i just got a new tube style sub with an internal amp in it in my trunk.....i put it in myself...it seems to work fine but whenever i turn up the volume nobb past about half way the way it starts to make a loud rapic thumping or poping sound wich continues even if the music is turned down.........DOES ANYONE KNOW WHAT THIS IS !!!! what can i do about it.........any help is much appreciated..