If its REALLY loud, you may have a component problem. First thing I would try is turning the gains down on the amplifier, as "more gain" is not necessarily better. It actaully is supposed to match the output of your radio to the amplifiers input. I would also check your grounds, even at the battery, make sure they are grounded at the same spot, as short as possible. Then try re-routing your rca cables. You may even try running on over the tops of the seats or outside the car on the ground temporarily to see if the noise goes away. If so, your interference is coming from the path you ran your RCAs down and they need moved...
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