Noticed that on my PC as well, bloody nuisance. If I turn my monitor off and back on Windows will automatically switch the default audio source to the monitor even I though I disabled the monitors audio.
This was never an issue in Windows 7, 8, 8.1 or 10 before the anniversary update and it's getting on my bloody nerves having to change my default audio after reboots or I turn my screen off and on. Other than that issue everything is perfect.
I'm using the motherboards Realtek ALC1150 and LG TV as a monitor.
Im assuming the TV is getting its sound via HDMI?
If so, what is setup in Nvidia control panel? It can sometimes default to HDMI audio unless its disabled in there.
Even if its not getting its sound from there still check.
I had the same issue and it was due to NVC, defaulting my sound to my main monitor which in turn changed the windows settings
