Help with line noise (Engine Whine)

I've done alot of searching on the noise issue. I have eliminated some(not alot) by following advice that some members have given in other posts. I have tried different quality cables and still not much difference. I have also moved the lines away from cables with power going through them and also not much difference.

I'm currently using a metal case, invertor, onboard sound, to a panasonic headunit with aux in.

I've done the following tests I could think of to help diagnose the problem:
With just the inverter on (truck not running) I get a very minimal buzz at max volume.
With PC on and nothing playing (mp3's etc) the buzz is overwhelming at about half volume.
With the truck running and pc on(nothing playing) the engine whine is there at all volume levels.

My inverter is grounded to a seat bolt in the back. I have tested this ground and it is a very good one. I've read about grounding the case and motherboard to the car chassis itself. My question there is what guage wire to use? Also some say the psu itself, isn't it grounded through the inverter? Should I ground it also?

Everyone says grounding to the same spot is the best way to go. Do I just run all the wires to the same bolt as my invertor ground or do I need a ground distribution block? Please excuse all the newbie questions I'm just trying to make sense of all of this. Thanks in advance for any help you can provide.

how do you know its a very good ground? is there any paint near that bolt? Bare metal is necessary. There are noise filters for this type of thing but they are usually a work around to a bigger issue. Cheap parts use cheap electrical components. Filtering is a big part of a good head unit, or other audio electronics. Power and audio cables obviously should not be next to each other.

The issue isn't with the ground being "good" or "bad". Moving the ground location, star grounding, etc. is just a band-aid fix. The problem is that your audio signal ground isn't isolated from the power ground.

You may want to consider using a power supply/inverter with better isolation, or maybe a high quality isolating transformer.

It doesn't always help, but a ground loop isolator is usually the first to think of, especially if you don't have high quality wires.

Dumping the inverter for a DC-DC power supply will also help.