This may not be classed as a bug, but there is significant noisy feedback when using this type of headphone with the REALTIME option on in the editor (when it is off there is no problem).
Headset used : Sony Noise Cancelling Headphones Model MDR-10RNC
Clicking out of UE4 has silent performance.
Clicking into UE4 produces considerable hiss and buzz in the headset, tied to clicking the mouse.
Pressing Ctrl+R toggles Realtime, and the feedback toggles too (except noise while moving the camera with mouse held down, which doesn’t go away).