I just hooked up a 1600 watt Ma Audio 6 channel amp. I am only using 2 channels for now though. But anytime I turn the stereo off while the ignition is on the subs make a really loud humming sound. What do I need to do to fix this? Is it because the amp is not turning off while the radio is off? Is there a wire that I can splice into to turn off the amp when I turn off the radio?

Thanks in advance.