make sure you have the sub wired correctly because if the amp is working fine then it should have to do with the amp cables. i would go over all your wires on your amp, make sure you have everything set correctly, and then make sure your amp can take the load its presented with.
its just a single wire coming from the amp but where ive connected it on the car there are other wires touching it! shall i move the ground wire to a place where it is not in contact with other wires? yeah infinity are GOOD ive got 2 sets of 6x9's, they give out wicked sound!