2018 Honda Accord EXL 2.0 GB 3way doors GB40/10 centre Helix M4dsp/M6 Sundown salt MMats + more
You know what I feel for you and your situation sux. 300 post and a grip of effort you have put out and no solution. I wish I could help. I say you find the quietest of all of the solutions and live with it. I would have quit a long time ago and just used headphones.That's interesting. Looks like in this case the DSP was picking up noise wirelessly from the battery, as it was located almost right next to it. I can definitely cover the battery with a piece of soundproofing foil. But I have previously moved the amp to the backseat, far away from the battery.
With the amp powered from the battery and the car off, there's no noise unless, for example, I connect that usb dongle to an exterior power source. Like when I plug the adapter into household outlet.
But if I power the dongle from USB port on the headunit, there's no noise (that's with the car off). But when I start the car, even if dongle is powered from HU usb port, I can hear a small whine, suggesting some interference is getting into the amplifier.
That's why I'm not sure if the battery can be causing it.
I'll double check again, but when I use my phone via rca adapter to send input into the amplifier, I don't have any noise or whine.
So maybe I'll just have to settle for using my phone via 3.5mm jack to play music.
But if the battery is causing any interference, what I'd really like to know if how to test for it. I haven't heard of having interference from battery if a filter is installed, like I did in my case.