Engine Noise With AV Multisource Switch

I have a 2000 Ford Ranger regular cab with a video monitor installed in the glove box (I know it sounds weird but works remarkably well), a Nintendo 64 game console (powered by an inverter) mounted behind the driver's side seat along with a 10" subwoofer and an amp. I have a set of component speakers mounted in the door locations which I use my HU to power. Now here is my problem: Next to the video monitor in the glove box, I have a multisource switch which allows me to press a button to switch between different audio sources. So far I only have two audio sources, the Nintendo 64 and a D-Link Roq-It MP3 Jukebox (independently powered by an internal battery). When the Nintendo is hooked up directly to the aux in of the HU, the sound is very clean, same thing with the MP3 Jukebox. However, when I hook both of these items up to the multisource switch, I pick up alternator noise when I turn the sound up. Any help would be greatly appreciated.

• First off, check the GROUND and make sure that all the connections are clean and secure.
• Next , check to make sure that you have not run any of the RCA wires in parallel with power wires. The power will induce noise which the RCA's will pick up and cause the whining.
• Post your results