Okay, I've had this setup for a while now. I'm running a kenwood headunit, 2 12 MTX subs, a 4channel MTX amp for my rears and fronts, and a monoblock for my subs.

Ever since I first laid all the wires and set it up. I've got interference while my car is turned on, only. I installed a new battery. Then tried to rewire the head unit directly to the rear battery, and while rewiring I accidently pulled out the wire between the two (front and rear) batteries, so the rear wasn't charging.

While the batteries weren't connected, I managed to remove the rev-related interference (loud buzzing noise), but I continued to get a constant interference (and loud) in the rear speakers. I installed a ground loop isolator, which removed the interference, but removed voices almost entirely, and distorted the music slightly.

When my rear battery ran out of charge, I realised the wire was disconnected, and reconnected the two batteries, and now the interference is back (including through the front splits, although not quite as bad).

Now, I suspect that the RCA cables for the rears may be bad. So I'm planning to buy a new RCA (expensive one, so good quality) and see if that fixes it. But it's not going to fix the constant buzzing, since I think that's coming through the main power wire. I have a surpressor on the power wire to the head unit...

But with all my attempts to remove this buzzing noise, I'm running out of ideas. Can anyone suggest what might be causing it, ways to fix it?

 

Are the power and RCA cables running down the same side of the car, or did they get run down different sides?

Nice short ground runs?

Might want to double-check your grounds.

 

There are numerous and I truly mean numerous possibilities for noises in your system. Your head unit and amplifier both even have couplings which prevent this problem, for all you know your headunit or amp coupling might have blown. It is not easy to test this on an amp, but try grounding your RCA wire shells to anything and see if anything stops, if so then you have a head unit issue.
Otherwise when you buy RCA cables, dont just go expensive, make sure they are shielded. Morons at best buy tried telling me these dont exist, so don't go to best buy and expect them to help you much unless you have people there who actually know their stuff.
As for the noise, separate your wires, RCA on left side and power on right, keep a 2 foot distance minimum if possible. Check where your wires run along, see if your wires run along any other wires at all, or grounds. Make sure all your grounds are on the same bolt, dont split them or else you get ground loops.

 

RCAs are running down the left side of the car, power wires are running down the right side of the car. They're all seperate.

Behind the headunit there's almost no space though, all the wires are crammed together. So I wonder if that might be causing it too.

My ground is about a foot or two away from the rear battery (which all the other grounds lead to). I've grounded to a rear taillight.
I considered it being the ground, but am not so sure now that it only happens when the two batteries are connected. If it was the ground, wouldn't it be happening even without the two batteries being connected?

 

your two batteries are creating a grond loop.... your tailight ground isn't good enough... get a self tapping screw and remove the paint were you are gonna ground it.... a ground loop is caused by resistance between two componets......( bad ground )... the best way to fix it would be to run a ground from your front batterey to your rear one.... hope this helps

 

Hm, I'll need to buy some heavy gauge wire to run a secondary ground between the two batteries directly. I'll check the RCAs then try that. Thanks.

 

Is your amp turn on wire on the power wire side of your car also? I made the mistake of putting it on my RCA side and it gave me a buzzing also until I fixed it...

 

Yeah, the control wire is running with the power wires.

Strangely though... I just went to test the RCAs, yesterday I was having a terribly problem with the rears only, and suspected a faulty RCA was causing that. But now it's stopped. Knowing my luck, when I get in it to drive it, it's going to start again and I'll have to pull the RCA for the rear out again.