static in rca outputs

I recently bought a 500w Visonik amp on Ebay for like $12, and I let my buddy use it for awhile.  It worked awesome for him, but he bought a new one, so I got it back.  Yesterday I bought 2 Rockford subs in a Q-Logic bandpass box that sounded AWESOME with this amp.  Now I got it hooked up in my trunk, everything should be perfect, but not only am I lacking a little bit of power, but my rear channel has static crackles in it when I get it above halfway up (Only when the outputs are plugged into amp.)  I hooked my RCA's up into the rear channel, just spliced them into the rear speaker wires.  Everything is all straight and that, so where is the static coming from?  Do I maybe have one line in switched?  Could that cause a disurbance?  Both subs are in phase, or so it seems, so other than the thought of having one input wrong, where else could the problem begin?