noise, lots and lots of noise

I just finished the install on my 08 Subaru Impreza 2.5i and it has more noise than I've ever heard.  I know what you're thinking, another thread about ignition noise...  Please, give it a read.

Ok, some background on the system before I get started.  It's all carry over peices from my last car, in the last car everything work well together.  HU is a Kenwood KDC-X590, front stage consistes of Boston Pro 6.5's powered by a Precision Power PCX-280, sub is an Image Dynamics IDQ12V3.D2 powered by a JL slash 500, RCA's are Streetwire's ZN9.  The install is very basic, HU is using factory power, ground and memory.  The amps have dedicated #2 power and ground run straight from the battery.  Also I have #2 wire going to the B+ and casing of the alterntor.  I'm not running any rear speakers.

Ok, here's what's going on and what I've tried.  With the key in the on postion, engine running or not, there is a ton of what sounds like ignition noise.  When the key is in the ACC position the noise disappears.  I can also hear this same 'humming' from most of the electrical components under the hood when the key is on.  The noise from the speakers disappears when I unplug the RCA's from the HU and I let the ends hang free.  If I touch the ends of the RCA's, the noise returns.  Using dedicated power and ground for the HU didn't change anything.  I tested for AC voltage while the engine wasn't running but the key was in the on position. I didn't get a reading.  Battery voltage is 12.6 volts.

Ok, so what could possibly cause this type of noise when the engine isn't running?  Should I run a ground from the body to the battery?  Would another battery be able to dampen this electricial noise? (I'm only using the factory battery)  Would a better HU be able to filter out the noise?

Thanks for any help.

Sounds to me like you may have a poorly shielded ECU and noise from it is being induced into the amp, the speakers or the speaker wires.  Locate the ECU and see if it is close to your amp or if any of your speaker wires are running over it.  You may have to relocate the amp or speaker wires.

The ECU is directly under the HU....  Do you know of any shielding methods?

Well, I wont be selling my 08 so that's out. 

A ground wire to the ECU case is a good idea, I'll give that a try tonight. 

Thnaks for the link.  Looks like a decent product and not too expensive.