the new PC now floats the outputs, for new GREEN rules, a floating input to any audio powered amp speakers
gets you 60 Hz AC power noise from the homes walls.
In effect your cable is now a noise antenna.
MY PC uses optical to the AMP speakers and never ever makes 60hz hum ever.
ever see a rock band member and tune up and with amp 1/4" phone jack hum as he lays it on the Guitar jack; bingo same deal. HUMMMM REAL LOAD TOO, with ROCK AMPS.
no 2 sound chips or cards do the same thing here, floating or not.
the fix is dummy load added to the jack pins to ground L/R channels. 10k ohms. or the the speaker side.
or use double shielded, 3.5mm cables
and make sure the PC power cables has good 3rd wire to the power cord end and wall jack greenwire not broken.
MY PC is all metal so no hum ever lands inside my PC, (fardays laws)
trick 2: is make sure the AMP end ground shield of cable as it enters AMP is fully grounded, most are not.
most are plastic, with no real ground,
buzzing is homes lighting noise entering that cable.
NO warranty answers by me.