Most GeForce and Quadro GPUs feature an integrated NVIDIA audio controller for outputting audio through HDMI or DisplayPort. If your graphics card is connected to a display which can receive audio through DisplayPort or HDMI, Windows may change the default audio output from your computers sound card to your graphics card as shown in the screenshot below:
To change it back to your sound card or USB audio device, perform the following:
1) Click on the Start button in Windows
2) Type "Control Panel" and open the Control Panel Desktop App which comes up as a search result.
3) In the Windows Control Panel, select Sound. You will see a list of all audio devices installed on your PC. Find the audio output you wish to use and right-click over the selection.
4) Select "Set as Default Device" as shown in the screenshot below:
5) Click OK to exit the sound properties.