ok guys i hooked up my system tonight. and everything gets power, but the sub barely moves, like theres almost no power getting to it. until i turn the volume all the way up, then it starts to go. the sub is a cadence cvlw 12-4 and amp is a cadence fx102. my rcas are hooked up the Rear audio out in the back of my HU. its grounded got power but im just stumped any help?