So I was able to reproduce this on my machine if I crank the volume of my speakers to their max (cranking to 11) and I can hear faintly in my headphones the in the videos above.
With a repro in hand, I tried a few things to mitigate it and discovered it’s totally independent of the audio engine AND the OS volume level and entirely dependent on the Slate UI and renderer.
Running UE4 with no audio device (i.e. xaudio2 is not initialized) produces no difference. Interestingly, running UE4 with no audio device and the OS audio volume set to 0 also produces no difference.
However, interacting with the Slate UI widgets affects it (sliding sliders, pushing and selecting buttons, etc). Interestingly, the tone/noise that occurs is reproducible/consistent with the type of widget hovered-over or interacted with. For example, for me, moving my mouse over any of Transform UI of an actor produces a particular noise vs selecting something in the content browser.
Tabbing out also fixes it so the cause is something that is activated when UE4 is “in-focus”.
I’ll create a JIRA for somebody from our UI/Slate team to look into the problem. In the mean time, turn down your actual speakers and turn up the OS volume.
I set my speaker outputs to about 50% and my OS output to:
Though note that above I said that OS speaker volume isn’t the dependent variable, it’s the hardware speaker volume.
Note that I hear the start happening at about 95% of my max speaker volume output.