Does the mic go directly to OBS? Or does it go to the game console first? Or does it split to both?
At any rate, draw a diagram of your entire audio rig. Where each signal goes, how it gets there, what happens to it at each point, etc. Then once you have that, look for loops and for multiple paths from the same raw input to the same final output. Both are bad.
Something that often trips people up is that the Desktop Audio captures the signal AFTER the device mixer. So it's literally a copy of what the *speakers* are doing (or whatever the device is), period. Notifications, apps, etc. If you send OBS's Monitor to that same device, it'll be included in the Desktop Audio too, and that's a loop.
