bad alt wine

[duece9s]

my factory battery location is in the trunk, and i  added a second battery, and i have had bad alternator whine for forever. + from alternator is on the right side of wheel well,and then follows rear seat. There is a bundle of wires that i run parallel to alt +. i tried to sketch them as normally routed, with the amps in roughly the right location. transition from dashed to solid is where they are above the trunk floor liner for +/-.  i was thinking about changing the RCA running on the drivers side from the front of the car, instead of passenger side.
pink:rca
green: speaker wires

blue box: sub 

grey: grounds

reds: +
long story short, am i experiencing this because of rca in proximity to alt +, or the mess of wires coming in/out of the amps?

[EricM9104]

Holy spaghetti.... I'd suggest, clean up your wiring first, get rid of that aluminum splice/whatever it's called going from your main batt ground to the secondary.

I'm sure there's either corrosion underneath the side post terminals, or inside of the boot (they love to corrode and not be seen).

RCA wires being close to your alternator feed will bring in whine, bad grounding will also introduce whines, any oddball grounds will introduce whine (ground loop feedback)...

Check your grounds under the engine bay and in the trunk area, make sure they have a clean metal on metal contact, no corrosion, no paint/etc...

[Loudsinglecab]

Why did you add a 2nd batt for that lil amp to begin with bro?
I would clean up the wiring just take your time and you will get it right...

[duece9s]

i found a loose ground as i had most of the wires out recently to put ferrules on the wires going to amp. Is adhesive lined shielding foil tape worth anything?

one of them is a MT-1000 (700@2ohm), the other is ZD-750.4D (400@4ohm). i got a second because my car has electric power steering and i wanted more reserve capacity. It starts like a champ in -20 despite both those batteries being at least 10 years old. 

 

edit; i'm going to remove that ground splice, going to sand the paint off of the bracket where the ground attaches to, and possibly redo the amp mounting to stack them vertically instead of beside eachother.

Edited October 19, 2025 by duece9s

[duece9s]

i rerouted the rca along the left side of the car from the radio so it doesnt cross the positive from the battery, got rid of ground splice, sanded paint off bracket where ground attaches. still sounds like crap at 0-25% volume.  do i need to move the ground shown in the first picture to somewhere else?

[duece9s]

so i've tried:

uplugging rca; no change

hooking phone up to amp with rca to 3.5mm; no change

moving both amp grounds to same spot; no change

rerouting 4 ga +/- to go thru the trunk mat all in the same spot infront of amp stack; no change. Rca's no longer cross over grounds

probed grounds between points A+B and it was 3.5mv.

is it something with my car being a unibody and the alt just being grounded thru the case?

do i need to add a hole to the trunk shell to ground both amps?

 

 

removing second battery and second amp did nothing

 

Edited November 22, 2025 by duece9s

[Joe X]

Power the amp with your trunk batteries disconnected from anything but your amp, use your phone connected to a 3.5mm jack to RCA cable directly to the amp.

 

This would eliminate any noise with the car on or off.

 

If you get noise with the car on but not off, the noise is coming wirelessly, that would indicate alternator damage or some other electrical system damage.

 

if you get noise with the car on or off you should try the same test with another amp, that amp could be damaged internally.