ground loop issue in a '94 chevrolet

Hi all. Here's the situation: I am a high school senior, and a thoroughly addicted audiophile. After reading on this forum how an external full range amp helps tremendously with sound quality, I decided to get one. The 4-channel: Boss CX-350. The rest of the system: 1994 Chevrolet Cheyenne Single Cab Long Bed 2500. 124 amp alternator. Pioneer DEH-P4000UB Head Unit. 2 12" Sony Xplod Subs behind the seat. SVC 4 ohm. Enclosure: 1.87 CF, stuffed with fiberfill. Has a dividing wall. Sub Amp: Sony Xplod 160Wx2. Bridged to 4 ohms. Sony Xplod 4x6 4-ways in dash. Sony Xplod 6.5 2 ways in doors. Custom fabbed (Thanks to Dremel.) And the aforementioned Boss amp. http://www.bossaudio.com/main/852 Amp power: 5 ga wire to a dist. block, then 8 ga to the 2 amps. Runs of 8 ga are about 2 feet long. Ground is a 5 ga on the Xplod and an 8 ga on the Boss. The classic whine has manifested itself in my full range speakers. Ground is to a seat belt bolt. I am sure that this is probably incorrect, but I am here for advice from the pros. Also, I have installed ground loop isolators in the RCA signal lines. The RCAs for the Boss are both shielded. So, how should I best go about eliminating the singing gremlin in my speakers?

Relocate your grounds to the same spot, make sure its bare metal (scrape away the paint). The bolts behind your seat, although easy to attach to, don't really make for the best ground points

merc250 wrote: ...and a thoroughly addicted audiophile.

And yet... Your choices for audio reproduction devices ARE the very bottom of the barrel! Sony Xplod and Boss Audio...?? "Audiophile"? Well, look at it this way. Your system will do or will have several things better than an audiophile stereo system... Distortion, noise, and a poor S/N ratio. If you can return any of that stuff, please do so, and return here with your budget. There are probably MANY products out there that will FAR outperform Sony Xplod and Boss Audio for the same or slightly more money.It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

The Boss can be returned. I will sell the Xplod subs and amp secondhand. I know of a potential buyer. Then my budget will be about $250, plus what I can kick in from my summer job. Suggestions for proceeding from here are welcome and invited. For the subs- I have the biggest box I can fit behind my seat there. The box is a 1.87 cf with a maximum sub thickness of about 5.5 inches. On a side note, Webster's definition of an audiophile reads "One who is enthusiastic about high fidelity sound reproduction." I am enthusiastic about acoustically pristine sound reproduction, and am simply seeking the best way to arrive at that point.

WOOOOHOOOO I'm invisible again.

No you aren't. I am going to return the Boss only when I get a replacement. The RCA repair will take place.

The Boss amp is not the problem. 

Not according to Haemphyst. I am trying to get the most quality for my very paltry high school budget. I shall do the repair.

You are the one who has to listen to it, the only person that can decide if it does what you want it to do is you.  Granted it is not the highest quality gear, it should do for a Paltry High School budget.