RCA buzz when head unit is off and cracks when turned on.

[hallurs]

Hi i set up a system in a 2012 Volkswagen Polo, 1x 12" woofer, 2x 6x9 speakers and two amplifiers. Running a 4 gauge to the boot, same for the ground that is connected to the chassis in the boot. the RCA was originally connected through a adapter that hijacked the signal from the front speakers and everything worked good except for a small cracking sound when the car was started, but it was really minimal and not through the woofer so i didn't bother fixing it as I was going to switch out the head unit.

Yesterday I connected a double din touch screen unit that has RCA outputs. I removed the adapter and connected everything accordingly, got the system plugged to the 12V cigarette lighter to make it turn on when the key went in the ignition as the original system is a Can bus.

Now I have the problem that there is a loud buzz from the RCA when the unit is turned off, you think this is a interferrence from the car electronics ? It only happens when something in the car is turned on or running. The RCA is for now running alongside cables on the passenger side, think that is the problem ? Might be able to move it further under the carpet so it will be standalone and no interruptions. Or might it be the ground fucking things up or something else ?