I’m having the same issue as well which pretty much ruined my video. Best example I can give is in my video of the echo it creates around 9:44
https://youtu.be/5QORtmhNrQU (WARNING there’s cussing in it)
Now I’ve tried everything that I can do to fix it but at the moment I’m thinking it’s actually my headset and not OBS. Cause the only changes I made to OBS for mic/aux was removed noise suppression. Since while recording Fallout New Vegas,I believe I had my headset volume set a little high then usual. By switching to my turtle beach for the PS4 and listening to a YouTube video with my headset volume on low,OBS doesn’t pick it up and my mic track doesn’t have the desktop audio.
Now before I came to that conclusion of needing to use another headset,earlier I went into my microphone settings on the computer (not OBS) and turned off echo cancellation I believe it was called. Which even with my desktop on mute for OBS and my headset mic on mute, the test video I did had a faint audio of a YouTube video that I had playing. So once I turned echo cancellation back on, that solved the problem as well.
Only thing I noticed that having echo cancellation on is that it creates a weird background noise that I didn’t want but at the moment I’m not sure what on my computer is allowing audio to be played on the microphone even though my headset is on mute.
Edit: Never mind,after posting that I still had the same issue where the desktop audio was faintly bleeding through into the mic track. After some trial and error,it was narrowed down to the splitter for my headset. Removing the splitter and using separate headsets and microphone, desktop audio is no longer in the mic/aux track.