could be usb bus noise maybe. have you tried using different usb ports? (or changing from say a usb 3 to a usb2?). likewise does it work on another device (pc or laptop via usb).
how about using a ground loop isolator? (for 3.5mm or usb). what you described doesnt sound like a ground loop problem but perhaps.
your thoughts on the ag1 (ad500x) are that its not worth the kind of money they charged (one reason i recommend going with headphones+mic pairs for them most of the time) but are you happy with the kind of sound or is there something lacking? it seems you may be a bit unhappy?
we can get them working on your system likely once we figure out the issue.
So I have tried all USB ports on the PC and they all work fine, except with the issue at hand. I did just hook it up to my laptop and it had the same mic issue except it was even worse as the mic picked up nasty static as well.
I do not have access to a ground loop isolator right now so I can not test that as of now.
So I think my thoughts on the ag1 may be a bit skewed due to the fact that I have used them with the DAC and without it they sound a bit hollow or lack luster. I knew going in that I am paying more for a mic+headphone setup but I took a leap as I did not find a good add on mic solution in terms of the extra cord annoyance, as nobody seemed to offer a good way to combined the cords or keep it out of the way. I would be open to a desk mic if I wasn't moving back to collage and dealing with a very small desk. However I did not realize the ag1 was a re branded 500x, until you told me in my previous post, which is a lower model than I expected.
What I am trying to say is if I can fix this problem I will probably be happy with this setup as I do not have to bother with an add on mic, but I still think about the fact its only a 500x.... There is a chance I could end up returning it, and I most likely will return the headset and DAC if I can't figure this out. If it comes to that I could try a headphone/mod mic solution. I just wish I could go with a open back headphone as I know they are a bit better and there are way more options, but as I stated before I will be sharing a small room and I hear they leak a lot of sound.
Once again thanks for your help! I am going to keep saying it as I don't want you to forget how much I appreciate it.