You might have it hooked up wrong, I know I did the first time around.
Your amp has two four pin plugs, you attach the head speakers to the left one and your sub to the right one. Think of pin 1 as your + and pin 4 as your minus on each set.
Your LPAD goes in between + on amp and your left speaker in the backbox. You then set the LPAD about half volume.
Hope that helps