Hello, i have a 2010 audi a4 quattro with the audi concert radio and bang olufsen sound system. I have an amp and sub hooked up in the trunk. Amp is hooked up right. Grounded to same spot as battery and the rcas are spliced into the stock subwoofer wires but when i turn up the gain on the amp all i get is loud bass at one frequency. Im so confused. Please help