I received a Dell XPS 13 (9350, i7, QHD+ touchscreen) two days ago. It is working perfectly except for the speakers, which start producing a considerable amount of static noise (different from the wide known coil whining, which is also present).
I was thinking that there could be something wrong with the speakers (wrong insulation?) since this happens even if I set the volume to mute on Windows. However, I have installed Ubuntu (from where I'm writing this) and there are no issues whatsoever with static noise.
I have tried to disable MaxxAudio and to update the Dell Audio driver on Windows, but the issue is still present. Turning the volume up and down does not help. I have also tried to remove Dell's drivers and use Realtek's, as well as updating the Intel iris graphics to the latest beta, but it doesn't work.
It might be useful to know that I have enabled the Fn+F7 shortcut on the BIOS, which "disables all sound and light producing devices" (it turns off the screen, audio and even the power LED). If I use this Fn+F7 the static noise goes away on Windows (and comes back as soon as I disable this mode). So my guess is that insulation is not an issue, since it would also happen in Ubuntu, and the Fn+F7 shortcut would not help.
I have tried to update the audio driver to the latest on Dell's website and to update Intel graphics driver to the latest beta version to no avail