Screens of all kinds send out electric signals, so I was not all too surprised when my boom-mounted microphone picked this up the other day. Below for example is the pattern good old trusty rtspeccy(1) shows for an old Dell I had laying around, with its power adapter plugged in and microphone pointed straight at the centre of the back of the screen:
My Librem 14 shows pretty much the same behavior with the same setup:
I would not read too much into the magnitude, although it is larger for the Librem, as it is strongly correlated with microphone position and distance to the screen.
But there is a difference, at seemingly random intervals in the range of five to ten seconds or so, the Librem 14 power adapter will give away a “click” sound and you can see a notable drop in magnitude across all frequencies for about a second:
The (seemingly generic) FSP GROUP INC power adapter is noisier than the Dell power adapter I had at hand (I can not hear any noise from the Dell adapter with my good ear), but it is common that power adapters give away noise. The clicking however I do find to be puzzling. It is noticeable even from a few metres away, but not that annoying as you can tuck away the adapter somewhere.
I am not an electronics expert so this could all be normal; wish I could compare the adapter to other Librem adapters. Still, I thought I would leave my analysis here in case someone else feel puzzled if they experience similar behavior.