I know this is an old thread but I had this issue and after about a full day of troubleshooting and research I solved the problem and thought I'd post to help anyone else in the future.
So it turns out (for reasons unkown to me) that the Realtek HD Audio Driver is the problem here. Merely uninstalling it didn't work though as the windows updater would keep automatically re-installing it when I rebooted. Here's what I did to fix the issue:
1: right-click the your speaker/audio icon in the task bar.
2: Choose Troubleshoot sound problems
3: Choose Yes, open Audio Enhancements
4: After the Audio Enhancements page opens, another window opens saying "We're going to try something". Close the Audio Enhancements page (you don't need to do anything there) and choose "Play test sounds".
5: Choose "bad" or "I din't hear anything", don't choose "Good".
6: Choose "restart later" when prompted and choose "Bad" or "I didn't hear anything" again.
7: Choose "Good: Use HD Audio driver".
8:Close the troubleshooter
Now if you go to your playback devices (the UAC prompt will still occur for now), the active driver should be "high definition audio driver" instead of the Realtek HD Audio Driver. Now once you have confirmed that:
9: Go to system settings.
10: Choose Apps.
11: Look for "Realtek High Definition Audio Driver" and uninstall it.
12: Choose restart computer now.
You should find that after your computer has re-booted, you will no longer receive a UAC trigger when trying to access your playback devices etc.
NOTE: I find the default windows audio driver works fine, but some people much prefer the realtek driver. It's your choice whether the prompt is worth using it over the windows driver or not.
Also just to note this also fixed an issue where I couldn't change my lock-screen picture/background.