ok.... when the volume level is set at 00 the subs are making a "thumop thump thump" noise.... its not very loud but it seems to mimic my engine RPMs. When i turn the cd player off, the noise stops. My amp is set to come on when the cd player is on. what could this be? how is it doing it? can i be stopped? and another thing is this just started last week and ive have the subs and stuff for about 3 months. thanks guys (and girls).