I have a quiet environment and a good microphone available, so I think I'll spend some time today recording what my unit sounds like under various conditions, just so we can get some references there.
-- EDIT:
This may not actually be useful, because I can't get my unit to produce any extraneous noise related to video playback. I've got a video playing in Chromium on Youtube in full-screen 1080p60 - which I understand would not be possible without hardware acceleration - and the sound from the speakers with silent audio playing (so the speakers are active, but being given a flat signal that should produce no sound) is only at the very edge of audible.
I can get the power regulator to emit a very audible coil whine by plugging in a USB-to-barrel-plug cable connected at the other end to a 2.0A power supply, but I suspect this would be a pretty obvious culprit and is also likely not very good for the unit.
-- EDIT:
This may not actually be useful, because I can't get my unit to produce any extraneous noise related to video playback. I've got a video playing in Chromium on Youtube in full-screen 1080p60 - which I understand would not be possible without hardware acceleration - and the sound from the speakers with silent audio playing (so the speakers are active, but being given a flat signal that should produce no sound) is only at the very edge of audible.
I can get the power regulator to emit a very audible coil whine by plugging in a USB-to-barrel-plug cable connected at the other end to a 2.0A power supply, but I suspect this would be a pretty obvious culprit and is also likely not very good for the unit.