99 Ford Expedition, noise problems

Please forgive the lenght of this post...

Im really starting to think this one has gotten the best of me.  Ill open up with a somewhat brief summary. 

Car: 99 Ford Expedition Eddie Bauer

Stereo: Eclipse 8443 Deck, Fosgate 1001bd Amp (Subs), Fosgate 851x Amp (4-channel), Alpine type X 6.5" components (front), Eclipse 6x8 3 way coaxes (rear), all knukonceptz wiring (4 guage to each amp, high quality rcas) run down opposite sides.

Started having some weird noise in the stereo like 8 months ago, thought it was some blown speakers (amp may be just a tad too powerful for those speakers, haha), warrantied out all four speakers at my local shop where I purchased them.  Got the new ones in and still heard the noise, these are brand new speakers keep in mind.  Started to think it was my amp, pulled my amp, bench tested it, seemed ok; put it in my brothers car, sounded fine; put my brothers amp in my car, his sounded terrible.  At this point I have ruled my amp out as a source.  Re-ground my H.U. and both amps, used a wire wheel on the drill to get the ground locations down to bare metal.  Still sounded horrible.  Went to my local shop and tested a ground loop isolater on it, nothing.  Used two g.l.i.s, nothing.  Used new rcas, no improvement.  Used new rcas without running them (just pulled the deck and ran them over the seats to the amps), nothing.  Connected the power and ground both directly to the battery, nothing.  Tonight I tried switching the deck out for a brand new alpine 9855 (just got it for free tonight from a friend, bids anyone?), really thought the deck was the only thing I hadnt switched out yet surely this would be the cause of all of my troubles, the noise is still there. 

I think this is a good list of everything I have tried, maybe forgot one or two things but you get the idea.  I feel like I have exhausted all trial and error tests and still cant seem to isolate the problem.  If I could at least find out what is causing it I am willing to replace whatever or re-wire Im just frustrated at this point.  If anybody has any ideas on other test please let me know Im willing to try just about anything, or if anybody has any thoughts as to what it could be.  Im really out of any and all ideas on this one, please if you can give me some insight I will be forever in your debt.

Oh the noise is sorta just like a fuzz, its horrible distortion at low volumes (anything below 1/2 basically) where you cant even hear the music.  If you turn it up you can hear the music just fine but its still there, presents itself as almost a white-noise in the background at high volumes.  Doesnt sound anything like alternator whine to me.  Happens when the car is running, off, driving, or parked, its basically always there.

Thank you for reading all of this, and hopefully for your help,

Jeff

I probably should have mentioned the charging system upgrades I have done as well.  It has a 225a high output alternator, an optima yellow top, and waiting in the garage for once I get this figured out I have an extra red top with a 200a isolater (this was in when the noise started, took it out to diagnose a charging system problem in my brother's car).  I have actually already cleaned the terminals on the battery (told you I probably forgot some of the steps I took in troubleshooting), didnt seem to make any difference, and those things are spotless.  I have already added some extra 8 awg to the big three, but it was just because I had extra wire lying around, i know I should really go bigger and that may be the next thing I try.  Any other ideas from anybody?

Thanks,

Jeff

yea for sure u always want to add the same going to ground as positive going out. example 4 ga in add a 4 ga ground. the factory 8 ga is only meant to run headlights etc...

The gains were fine for a long time going up to this and I actually did reset them at one point, because that was also one of my first guesses.  The speaker wire idea is actually a really good one, that seems like the only thing I would have accidently changed without realizing it, I will go through and pull all the speaker wiring and rerun and reconnect.  Anything in particular I should be looking for?  Just exposed wire? or wire that is in some way grounding out?

Thanks for the info geep, I honsetly would have just started pulling wires and re-running them, really should have thought of this but thank you for saving me hours on this.  So when I ohm them out I just get a 4 ohm reading on all of them correct?  would I see something closer to 0 ohms if they are in fact ground out on a given channel?  I will check all of these the second I get a chance to, that car is at my other house which is about 40 miles away so I probably wont get to check on these and let you guys know what happens for like a week or so.  Thank you for all of the help so far, I really appreciate it.

Jeff

sk8ingsmurf wrote:

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would I see something closer to 0 ohms if they are in fact ground out on a given channel? 

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maybe, maybe not. A black oxide screw going through speaker wire into a painted surface may not have 0 impedance to ground. It could have just enough potential to cause noise but not enough to change the impedance of the speaker.

He's right, it won't necessarily be 0 ohms, but it will be significantly less than 4 ohms.  First ohm the speaker wires while disconnected to read the speakers individually.  Then check the leads seperately for a short to ground- touch one probe to a speaker lead, the other to the amp's ground terminal.  Be sure to do this with the leads disconnected from the amp though, so you don't get a false reading.

What geepherder said.

With the speaker wire disconnected from the amp there should be (in theory) infinite impedance to ground. A finite impedance is a problem. 0.1  ohms = problem, 4 ohms = problem, 100 ohms = problem, ect.

Oh, if you have any passive x-overs you will need to do the same check between those and the individual speakers.