Pretty common problem on builtin sound cards, even now. It's just very close to the noise source.
Shouldn't really happen on USB DAC, it should have enough filtering to get any interference injected by power, and enough shielding (and just being far away enough from machine) for other EMI
Yeah this is the main reason to use a USB DAC. I guess you get marginally better sound quality (more noticeable on expensive studio headphones that need more power to drive them) but better isolation/removal from the noise source is the main reason I use them. Especially relevant because in my travel I'm often in countries that don't have ground plugs in their power sources.
Shouldn't really happen on USB DAC, it should have enough filtering to get any interference injected by power, and enough shielding (and just being far away enough from machine) for other EMI