Crazy car electrical/audio noise issue!

Listen to this.. I was having some system noise aka background noise in my system (car computer + amp + speakers) and so I have been trying to isolate the issue for some time now (several weeks). The noise is there when the car is off -- heck, even when the car computer is off but getting power fed to it. So I finally heard about "ignition buzz" so I decide to try bypassing the ignition and just hard-wiring the stereo. So I do and voila - no noise! BUT, as soon as I turn on my ignition (note: not the engine, just acc.) it is back. Then I shut off my car. Then it is still there (cuz computer + amp is still hard-wired). So this is weird now because the circuitry which is causing the noise is STILL closed and the noise persists yet it was not there before I turned on the car. Then I open my driver's side door and close it. Voila - noise gone. So something weird is happening. I haven't gone messing with any factory wiring -- don't worry, just basic car audio wiring, like running a wire from the batt to a distro block to my amp + pc, and then a ground wire from the chassis to my ground distro block to my amp + pc. Any idea what could possibly be causing this?? This is crazy!! Thanks, Kevin

What kind of car is this? It sounds like this car has accessory power that stays until the driver door opens. I don't know which wires you went to or what kind of computer you're talking about but if you ran an amp and are driving power to a device that can create feedback, that would answer your question,much like turning on a flourescent light in your car.

2003 Nissan Maxima I tested it again and opening/closing the door doesn't always make the noise stop. It's almost like when I turn on acc. it changes the grounding pattern for my car, and then that causes the feedback noise.

Did you install an aftermarket amp? If you are running an amp I would suggest turning off the amp and running a speaker straight to the HU. If the noise is only through the amp, you may have to check where you ran your RCAs.

I have a 4-channel amp and my pc all in the trunk. The RCAs are not touching a thing and are very high quality cables. They are only 1m long, too, since my pc is right next to my amp. I verified no wires are crossing anything. Please understand I have been troubleshooting this for weeks. I know the noise is coming in from the ignition.

Electrical noise with the engine off but the ACC on is not ignition noise, it is a ground loop.  The weak link is probably your car computer.  Try connecting the computer power ground and case ground directly to the battery negative terminal, and run a new HU ground to the car's chassis - do not use the ground lead in teh wiring harness.  Measure this conenction with an ohm meter and verify it is less than one ohm to the battery negative terminal.  Also ensure your amp has a good ground to the chassis.Support the12volt.com

we need mo info Si!   what king of car pc? is it a home pc plugged into a converter? do u have it hardwired? if ur ground changes when tha doors open maybe u spliced into a door trigger?

The PC has a 55w DC powered (12v input) power supply. It is kind of designed to plug right into a car. I ran some extra ground wires to the (-) battery terminal, but it was 20awg wire, so perhaps it was not enough. I am going to change my distro block ground location also, since I used an existing bolt and sanded away paint, rather than drilling with self-tapping screw which would probably yield better connection. I tested with a voltmeter and found good continuity through the current ground location, though. I have no head unit, btw. I did not tap into any wires, except one for the remote turn-on lead - that is all. I also need to hook up some headphones to PC sound card and see if I am getting this noise -- maybe it is only present when amp is in the loop -- then again, maybe you can only hear it when amp amplifies it.. *sigh*

Sounds like your inverter is generating noise. Unplug it totaly and remove it from the car and see what happens