Help with how to properly ground

I have my PC system in, up, and running but.....the audio and video quality is suffering. Let me first give a quick description of the system. I have a set of RCA's, s-video, 2 usb and 1 firewire running down the passenger side together to the rear floor compartment. There is a 12ga and a 16 gauge power running down the driver side. The video and audio all run to the avelectronic box under the passenger seat. I have a dvd in the center console also hooked to the ave box. The dvd, ave box and two P.I.E. amps are all grounded at a bolt holding the NAV unit to the floor. The PC is grounded back in the rear floor compartment. I have two case fans also wired to the this ground and the incoming power wire.

So I have this bad engine whine after I get everything hooked up. So after a trip to radioshack for a noise suppressor I find a ground loop isolator and see that is what I probably need since I have two seperate ground points. Well that helped a lot but I still have some whine and the audio quality just isn't what it should be. It sounds kind of distorted and makes some craking noises. The video is also not great. The picture is not real stable. It has some flickering going. At first I thought maybe it was just the nature of the PC but I tested it out by hooking it to my 32" home tv and stereo and all is good there so there is definately an issue with the car wiring. I ran a seperate rca cable instead of s-video in the car and same thing. I don't have any of these problems with the audio/video coming from the DVD player, so I am deducing the issue is before the signals get to the ave swither box from the pc vs. on the output side.

I'm guessing that there is a ground problem with not having a ground tied together with all the components. So how should I ground eveything correctly? Should I run a 12ga wire connecting the ground point in front to the one in the rear? or do I need to tie everything to one ground point? Right now I have everything crimped because I can't for the life of me get solder to stick to the wires. I think the crimps are tight though. The other thing I'm going to change is to hook the fans to their own ground. I bought decent AV cables that were shielded, not the expensive stuff but they weren't exactly cheap either.

Anyone have any suggestions or recommendations on the proper way to handle the wiring? thanks.