I've searched and read plenty of threads on this, and I've tried quite a few things to mitigate the whine, but nothing has worked yet. I'm running out of ideas.
The vehicle is a 2018 Nissan Frontier.
First thing, here is a diagram of my system as it sits now, everything is OFC including the 12ga speaker wire -
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I am running active from a MiniDSP 2x4 to a Sound Ordnance M25-4 amp. Previously (before I had the 2x4) there was a whine issue but I believed it to be resolved. I was able to get the grounds to where the whine would only be introduced just over half gain on the amp. Hiss and other noise started to get introduced at this level as well so I assumed it was a cheap amp doing what a cheap amp does. At this time I was running active from my head unit which was OK, but like everyone else, I wanted to tune with REW and have much more control, so I bought a MiniDSP 2x4.
Once I got everything installed and setup,
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I started up the truck and was immediately ear raped by the sound of a banshee. This shit was LOUD. I immediately turned off the truck and turned the gains all the way down, and started it back up. There is still very audible whine with the gains all the way down.
This is how it sits now, I haven't used the system in the truck since Saturday, other than for testing purposes.
Things I have tried so far:
--3 different RCA's. Current ones are double shielded expensive-ish. I've run them outside the install with the same result.
--Moving the amp ground to a thousand different places. I finally found a good ground on a bolt on the seat belt mount, NOT the seat belt bolt itself. This ground measures between .0 and .4 ohms
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I have also moved the HU ground just as many times as the amp ground. I eventually settled on a ground that measures about .8-.9 ohms. Not ideal I know, but I quite literally cannot find a better ground than that.
Now, with the grounds. There is something weird as shit going on with them. With the head unit ground, when I initially connected it, was reading less than an ohm. I measured it again the next day, and it was reading 19ohms! So that got me to thinking, that maybe even though this is a new-ish truck, maybe there is something weird with the chassis grounds.
I go open the hood and see this bullshit, I did not see a grounding strap anywhere else so this appears to be the engine to chassis ground -
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WTF Nissan...
It was reading about 8ohms. I used some spare 8ga I had laying around and put it on there. The 8ga wire measured 0 - .1ohms before I added it. It now reads anywhere from 1 to 2 ohms connected. I did notice that it's grounded to a bracket...I think I will add the ground directly to the block and bolt the bracket over it to see if that may help.
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Just for the hell of it, I added some 8ga from the battery to chassis but I don't believe it made much difference as it was reading well before adding the cable anyways.
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Both locations were cleaned to bare metal which they weren't from the factory for some damn reason. This did dramatically cut down on the whine, but it is definitely still there and 100% unacceptable. I don't really want to do the Big 3 upgrade, once I'm finished I'll be 1500 watts total and the vehicle is still under warranty. I'd rather not take the chance on something like changing the electrical and voiding the warranty. If it becomes necessary, I'll try to install it all so that it is easily removable I guess.
-- I picked up a 3.5mm to stereo RCA cable and hooked up my phone. Pretty much 100% quiet. There's a little noise that starts to come in at around 75% to 80% gain, but I find that to be acceptable as even at 100% gain, you can just barely hear it.
EDIT:
--I forgot to mention that I also did the old Pioneer PICO fuse grounding method with no change, as well as ran a ground to the chassis of the head unit.
I've posted on quite a few forums and have gotten many suggestions which I will outline below, but I wanted to see what everyone here thinks.
I picked up a ground loop isolator even though I really do not want to use one. I'd rather fix the issue and have the least amount of components in my system as possible, but it may turn out to be a necessity. I figured that since when I plugged my phone into the DSP directly there was virtually no noise from the amp, that it must be upstream of the amp, meaning the head unit. I wanted to see if the ground loop isolator will eliminate it.
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
--On Reddit.com/r/CarAV a user suggested I get one of these
https://www.amazon.com/Behringer-HD4...7317&s=gateway and install it before one of these
https://www.amazon.com/Install-Bay-C...sr=1-1-catcorr. I understand the concept of cleaning up the signal and then boosting the voltage back up, but adding additional components doesn't really entice me. I also wonder if just the Behringer HD400 by itself will work fine, as the MiniDSP is incapable of outputting more than .9v to the outputs anyway.
--It has also been suggested that I ground everything to the same point in the cab. As you can see in my diagram, the head unit, and amp grounds are not connected. I can do this, but the ground would be about an additional three feet. I DID try to ground from the amp ground location to the HU ground location, but I do not think that is correct and it didn't help anyways. Maybe I need to bypass the current amp ground and go straight to the HU ground, but this is going to make my amp ground about 3 foot long.
--Others have suggesting drilling through the floor pan and grounding directly to the frame, but come on, it's a new truck with less than 20k miles on it.
--Something like this has been suggested as well -
https://www.amazon.com/Jensen-CI-2RR.../dp/B00ASVWYCS which is very expensive and looks similar to the Behringer HD400 I posted earlier, but if it works without changing the audio signal at all, as I'm reading from looking into it, it might be worth the money.
Hopefully, someone has can point me in a direction that I haven't thought of yet.
