Putting a DI between the computer headphone out and the mixer should
take care of noise introduced through that analog connecting.
I would go with a passive transformer based DI, the amount of true isolation
with an active DI can vary from DI to DI.
With most DI’s you would need to use the XLR inputs as the DI’s output closer to
a mic level signal and if you using an active DI you will need phantom power to
operate the DI, some will take a battery.
The ST1 and ST2 inputs are unbalanced, the channel line input jacks are balanced.
It’s too much; I’m just going to live with the noise, can’t seem to get rid of it after 4 pages of forum posts. Since the noise isn’t heard on the Zoom call, it’s not getting transmitted via the USB in, so as long as the caller doesn’t hear it, then I just can’t worry about it. It’s annoying to us to hear the whole time, but it seems like a no win situation. Thanks for your help though.
Troubleshooting via an internet forum can be tough.
Where are you located? Maybe there’s forum member close by
who could help you with some in person troubleshooting.