I did some research for myself, and noticed it wasn't hearable when plugging in either one of of my headsets. I use active KRK RP5 speakers, which have a dB dial on the back. I've set this to a very high value when I bought them and just kept the Windows volume down. However this was at +3dB, thus amplifying any static that came in from the PC.
There is still a static noise in my PC, but I've toned down my dB dial to about -10dB which is hard enough when I put Windows on maximum volume. But now it doesn't amplify any sounds that come through the board. So not an actual solution for the problem (leaking signal) but at least I can game without any annoyances