I tried everything, can't get rid of this ground loop
Car: 330ci BMW
Battery location: Trunk
PSU: Opus 150 - 10 gauge wire over 5 feet direct to the battery - wire resistance to terminal = 0.1 ohms (basically 0)
AMPLIFIERS: 3 amps, 1 crappy jensen amp for the rear, 2 nice esx amps for front and subs - 8 gauge from each amp to a T block and 4 gauge right to the -'ve battery terminal - wire resistance to terminal = 0.1 ohms (basically 0) - ground length (5 feet)
WIRING: OPUS and AMPS have separate wires
PROBLEM: I get a constant ground loop buzz in the rear speakers through my crappy jensen amp. My quality ESX amps do not have this buzz. On my JENSEN amp I can hear either the CPU fan or Hard disk spinning on boot up and when I move the mouse it makes a additional scratching sound in addition to the constant buzz.
WHAT I HAVE TRIED:
1) unplugging the line input to the card and muting everything in windows.
2) measured all resistance to make sure it was the same across all wires.
3) running my jensen amp off a portable cd player and house power adapter has no buzz.
4) I tried running my computer into my earphones to try and isolate if it was my soundcard that was putting out the buzz or if it was a combination of amps and soundcard. The earphones had no buzz making me think it is a combination of computer with amplifiers, which confirms the ground loop theory.
5) I have tried running the jensen amp, with the ground loop problem, being powered off the car 12 volt but feed a source from a portable disc man running on its own batteries. No ground loop or buzzing.
6) Update: ESX amp testing. I tried the ground loop isolator on the ESX quality amplifiers and there seems to be no change in the audio except for a slight dampening of the fq range. So it would seem that the ESX amplifier ground techniques are far superior to that of the JENSEN's. Outcome was that it sounded better without the filter.
My thought processes is this. At first I thought my soundcard might be passing noise to my amps through the 3.5MM jack ground. But my earphone test should have picked up any ground loops. So, I think it has to do with the soundcard seeing two separate ground paths back to the battery. 1) the soundcard is grounding back to the battery through the opus's ground. 2) then the soundcard now also has a ground back through the RCA's on the amps in the trunk, which then follows a different ground wire back to the battery. So now the soundcard sees 2 different ground paths and by using both paths it somehow picks up noise in the process (I don't see why since both ground wires have the same resistance). This could be causing some weird feedback loop that can only be explained by the crew of the star trek enterprise. The only problem is that my esx amp is not affected by this ground loop. So the only thing I can think of is that the ESX amps already have some form of a ground loop Isolator built in and the JENSEN does not.
To try and fix the above problem I have used a ground loop isolator, which breaks the ground connection between the rca's from the soundcard to my amplifiers. This FORCES the soundcard to be grounded back through the opus and for the amp to use its OWN ground wire. This stopped the ground loop on my JENSEN amp to the best of my ability to hear anything.
I am almost 100 % sure this is the problem now. Let me know if this makes sense or please share any other ideas.