D10, Mixer, Computer Ground Loop Nightmare

[MazeFrame]

I have a Mackie Mix12 hooked up 4-way to my computer (3 directly with analog, one via Balanced from my Scarlett 2i4). Setup

Yes, you have a mighty ground loop.
Behringer HD400 or ART CleanBox between mixer and computer should do. (Both require stereo to 2x mono 6.3mm Y-cables)

Could try a transformer isolator like the ART DTI

@burning_lemons

I thought maybe it could be interference, so I threw some ferrite beads on my cables and that seemed to do the trick. […] a high pitched whine would come, then go away (quiet down significantly?) about 15 seconds after stopping whatever the source of the sound was.

Inductors (your ferrite beads) resist a change in current. Analog audio is transfered as voltage with minimal current flowing. I am 80% sure this is the cause of the ringing.

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@burning_lemons

One thing I have found out is this mixer is pretty loud noise floor wise.

Interesting.
With my headphone amp (ART HeadAmp4 → M40x) at normal listening volume, pad switch pressed +10dB on the channel and +10 on the main, there is very low noise for me.

@burning_lemons

If you have any suggestions for mixers, feel free to let me know.

Depends on what you want to achieve.