EVGATech_LeeM What happens if you switch to the Line-In input?
VivicectorI have done some tests on the electric noise in the mic and rear channel issue recently. Here is the result: The noise is only around when my headphones (5.1 physical ones, with 4 jacks) are connected to both the main and additional card. Its all clear if only the add. card is used (no front channel or mic). Its all fine with simple stereo headphones mode. But when I link both cards with my headphones, the current starts flowing between and noise appears. Its not specific to any special port, its just a factor of lower resistance path.So, its some kind of a Ground Loop issue, may be connected with power unit or computer casing or generally bad grounding of the house.
EVGATech_LeeM I can see how that could create a ground loop issue. Let me check with our team for solutions.