I’m still getting some noise while listening to headphones now & then, I tried to reproduce with some test tones and quiet music today but I didn’t notice any noise on these tests.
FWIW I tried with nothing plugged into any port except a short stereo 1/8" cable going straight into a field recorder.
I made recordings initially with test tones at a moderate volume, but I redid the tests with very quiet signals afterward. Test tones at 200, 400, 800, and 8000hz, then a linear sweep from 2hz to 20khz. (FYI the oscillator I used doesn’t prevent aliasing distortion, so that’s present in the recordings, but the noise we’ve been discussing is nothing like aliasing distortion so I didn’t feel the need to use a bandlimited or analog test tone for this…)
I think I’ve only heard noise when plugged into power, and I’m sure I was doing more than just playing a test tone when it happened. I also generally use the laptop with a wired mouse, so I’ll try these again later when I’m working on something on the laptop with a mouse plugged in too.
Test tones, recordings, screenshot (just to show what was running at the time of the recordings, and the general battery level) and photo of how the recorder was hooked up are all here in case anyone is interested, I’ll try reproducing again this week!