alpine 7893 in 2005 civic, no sound

I've installed an Alpine 7893 into a 2005 Civic EX. It powers up fine, but when I turn the volume up past 3 or 4 the sound will start to flickers and then goes out all together. Turning the radio off then back on doesn't make the sound come back. The Alpine is simply powering factory speakers, no amps. The sound will stay if the volume is kept low, but even that only last for a few minutes tops. All speakers pop with a 9v battery, they all read 4.2 ohms, they all worked fine with the factory radio. I've changed the ground to one better than the harness ground but that didn't change anything. Any ideas guys?