Well first of all that is the WRONG way to hook up an amp. Ground the amp to the body, not back to the other amp. Secondly put a power distribution block in front of your sub amp and run 2 power lines from it. One to the sub amp and the other to your 6x9 amp. Third make sure your RCA cables from your head unit aren't running parrallel with your power cables and definatly not touching anywhere. You should get triple shielded cables and get them long enough that you can run them through your car like a snake, not just in a straight line.