Noise issue

We had a problem with some noise in a recent large system that we did, and I wanted to ask you guys a question.  The install was in a newer Expedition and included a fully powered system, flip-out screen with navigation, etc.  The amplifiers are mounted behind the back pannel and are very difficult to get to. 

The noise is a hissing sound in all the speakers, can be heard when the volume is all the way down, and seems to be louder in the rear speakers than the front.  It is also independant of the vehicle being on or off.  The gains on the amplifiers are set correctly (around half way up).  When I unplug the RCA at the deck, the noise completely goes away.  Doesn't that prove that the noise isn't being caused by the amplifiers or RCA's?  After all, the amplifiers are still on and if the noise was being induced into the RCA's, then it would still be amplified when the RCA's are unplugged up front.  I did the amplifier install, and want to prove that it isn't my install that is causing it, preferably without having to remove the back pannel to get to the amplifiers. 

If it helps, this was all used equipment when we installed it, including the RCA's.  But it's all good equipment (Pioneer video/Nav, JL amps, Focal components)

Have you tired stringing some RCA's through the car, not installed, to hear a difference?

I still wouldn't rule out noise induced by the rca's as the magnetic field has lapsed when thay are unplugged therefore noise cannot be introduced any way.

Do you have a common ground for your amps, or are they in seperate locations?

That was the next step, but I wanted to avoid that if possible as I would have to take off the back pannel.

They are both in the same location.

I didn't install the head unit, but I'm betting that the factory ground is being used.  We have quite a few things we could still check to get rid of the noise.  But as I was the one that installed the amps, I wanted to prove that it wasn't my work that was at fault.

Oddly enough one of the installers suggested that, so I tried it and it didn't seem to help any.  There is so much stuff connected to that thing, I'm not surprised there is a little noise coming through the system.

Yeah, and you can also try linking the amp ground to the head unit ground as well, but I do think it's the deck.  Have you tried another unit?

'Attaboy, way to prove your install wasn't at fault.  The shop I used to work at was occasionally accused of being a "hack shop", to which I replied, "I'm the only hack in this shop."