Car stereo buffs, please read.....

I just installed a system into my 2000 accord sedan and the trunk vibrates too much. I put in a 500w Performance Technique amplifier, connected directly to two 12'' Kenwood subwoofers. I've taken my trunk apart looking for whats vibrating. After hours I fixed vibrating between two rods that control the trunk's door. The next major source of vibration is outside, above the license plate. I have no idea how to sound-proof it. Does anybody know either how to fix the vibes myself, or of a place that will do it without sacrifing an arm and leg. Thanks stereo buffs