You're getting fequency sent from the head unit (weather it be intended or not intended) and the amplifier is just replicating that fequency with a/c attached at full volume.
or...
your amp's singal inputs are fubar and it's still sending a fequency to the sub at full power until the sub smoked
out in Waco eh? I used to live in Lacy-Lakeview for a few years. It sucked. //content.invisioncic.com/y282845/emoticons/crap.gif.7f4dd41e3e9b23fbd170a1ee6f65cecc.gif