Ok so with the gain settings at the same for both front and back speakers, the back speakers sound a little louder and more powerful. Both pairs are Alpine Type E. What could possibly be the reason for this? How the amp was wired (I had a car audio store set up my amp)? Also when my I turn the gain knob to a high level the front speakers start to crackle/pop, but not the back speakers, at the same level of gain. Please let me know what you think.