So I have this setup. I'm powering the udoo and an amp from this battery pack: https://www.amazon.com/gp/product/B00DN0KBXU It's actually pretty darn solid. I saw in another thread people were wondering how to power the udoo. This has got at least 8 hours for the udoo sofar and I'm at like 68%. It's actually overkill. In anycase, when I connect the the Amp (which drives a speaker) to the udoo I get a low high pitch buzz and some crackle. These components independently are fine. Different input to amp and udoo to different amp. It only buzzes when the 2 are connected. Right now my idea is it's some sort of back feed. I'm not sound enough in my electrical capacity to figure out where. Trying to google this has been difficult. I'm going to try putting rectifier diodes everywhere (like everywhere even on the 3.5 mm). Every time I order something though it sets me back 2 days, so any ideas are super welcome.
I know it solves it. I did indeed try that. I can go the second 12v route, but it adds weight as well as ruining the aesthetic of my design (not that it looks amazing anyhow lol). There's gotta be some sort of broader electronic theory that tells me what this is. I have two separate consuming device's and a single source and something somewhere should prevent whatever is happening. Do I need a resistor somewhere, is something not shielded? I'm hoping that there's a guru that can tell me what's happening. Otherwise in my mind all I need to do is make sure that one of the consuming devices is directionally isolated and then hopefully it works.
I've noticed this indeed with my monitor setup. Like @waltervl, I think you need a ground loop isolator. I haven't tried it myself as my solution doesn't actually use audio yet.
I think this is it! Thank you very much waltervl! I still gotta buy one. I built one, and it helped. The ones you buy are made for this and I think will be more effective.
