Nividia control panel should give you the options to check in on what GPU is set to run games. You should be able to set ME3 as running ONLY on Nvidia gpu, and if not there(but it should be) then you would need to check in at your Hardware settings in your control panel. You would be looking to set power profiles for performance and NOT any kind of battery saving. I don't know how to get into your sounds for your system, as I have never used Win 8.1...but it SHOULD be accessed by going into your control panel and choosing system/sounds and nosing through properties and settings in that branch. Also changing audio format, or quality levels may help too...ie in control panel settings for sound you should be able to find a listing for CD quality, or DVD and different sampling rates for each...Also changing the sound settings in Mass Effect 3 sometimes helps too, cutting some off or on....
Nvidia has sound drivers that are part of their Video card driver set...I don't see them on your DxDiag file, but just wanting you to make sure in your control panel and listed hardware devices that you didn't have them ticked.
Have you tried a clean boot of your PC??https://support.microsoft.com/en-us/help/929135/how-to-perform-a-clean-boot-in-windows
If it still acts up in clean boot, and everything is set right, then it sounds like an issue with your drivers and the game...or something in your hardware, drivers and game.
If it is clean on a clean boot, then it is a program cross interference.