I remember 15+ years ago reading about certain laptops (Dell?) that you could 'hear' scrolling on websites, somehow the video chip was interfering with the sound chips. I had one at the time it was pretty weird.
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
Just ordered a hat for my Raspberry Pi with optical out, with a plan to make that my main music streamer. Excited to see if that works out!
All the cheap boards have neither. Most of the high end boards have both
The trick is that your 3.5mm connector only needs to connect on the sides, so the end of the jack can be open for light to be transmitted.
This was seen pretty frequently on laptops for a while, but I think two things doomed it. One, most people just don't use optical. Two, there's nothing to advertise its existence. If you do have one of these ports, you probably don't even know you could plug an optical connector in there.
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It sounds exactly like the reads on a physical hdd, which is silly because it has an SSD. Haven’t figured out what it is yet.
I remember the BBC Micro doing the same thing when I was a little kid during certain operations, it always sounded to me like it was "thinking". :)
If power lines run anywhere near the sound lines, you are just asking to pick up interference whenever the computer does basically anything. It doesn't take too much of a pulse to be picked up. For a 3.5 jack, the voltage is anywhere from 0.002 to 0.5V. Even a pretty small induced voltage will be audible.