did you upgrade the ground to the battery, chasis, intake etc? I had terrible noise in my car also but ran 4ga from batter to HU/amps for both ground and power solver the problem.. also if you have external amps make sure they are grounded to the same point as the HU. Its really strange that there is noise there when your car is off however.. you might want to put a meter on the battery and see what its doing.. could be the battery. or a loose/pinched speaker wire somehwere.