"if I open a video game full screen, the noise completely disappears."

At last, ... a real use for a video game, huh?

The problem you are experiencing is because you are unbalancing the Preamp to the Recorder. So, my suggestion in your situation would be to take the XLR output from your mixer and feed that into the XLR microphone input of your Audio Box. You would then crank down the level, completely, also disabling the Phantom power on the Audio Box and also engage the pad switch for each input.

What you are hearing is a good deal of clocking noise. And also because, the computer is not set up properly as a dedicated recorder. Many programs that are running in the background are causing clocking noise issues. Some worse than others. Virus software, programs trying to access the Internet for update purposes, scheduled events such as automatic virus checking and defragmenting programs, all that stuff. Some of that stuff can be disabled from starting up or running on a PC running Microsoft Windows if you go to your start menu, run selection and type in MSconfig. Then pressing enter. That will bring up another window where you will see a tab that indicates " startup ". You would disable everything and I mean everything. This keeps these programs from loading and running until you choose to do so from the desktop or the programs menu. Then there is also the issue of virtual memory paging file. That too has to be modified so that it is not causing a dynamic caching but instead a static caching with a single number figure, based upon internal RAM memory which will actually indicate how much RAM memory you should punch in. Then you hit select to lock in a static RAM cache. So you need to go to our previous stickies here at Recording.org to look into how to properly set up a computer for music recording purposes. Generally that means certain settings have to be changed, other programs have to be disabled from running in the background a whole lot of stuff.

Then there is also the issue of ground loops between the audio board and the computer that can also worsen your situation. There are good ways and bad ways to eliminate that ground loop between the audio board and a computer. The audio board should remain grounded to the AC mains. With the computer plugged into the same outlet as the audio board you may be able to simply utilize a simple 3 to 2 ground lift adapter available for $.40 at the hardware store. Because of your stage of knowledge and proficiency, you don't want to start lifting grounds on your audio cabling if you don't know where and what to lift. Most computers today utilize what is known as a switching power supply. Older power supplies utilized a transformer which offered some isolation from the AC mains to the circuitry within the device you are recording upon. Switching power supplies are less expensive, extremely lightweight and generally can never be repaired but only replaced. So dealing with those can be problematic frequently requires lifting the ground on the computer power supply. There can be dangerous repercussions if not fatal ones if not done correctly such as plugging the audio board into one AC outlet and the computer into a completely different AC outlet fed by a different circuit. You should have no problem plugging them all into the same circuit.

Oy vey Maria is one of my favorites to record. LOL
Mx. Remy Ann David