Outside stereo speakers

If you have cut out the interior speakers from the circuit then the only other thing I can think of beyond the input volume of the ipod as mentioned above is that you either have a loose connection somewhere or the speakers or switch you installed are faulty. What happens if you swap the outside pair for one of the inside pairs? If the distortion follows the speakers they are likely faulty. If it stays outside then some part of your wiring is bad, either loose connection, cut going through aluminum and shorting or bad switch.