This issue can be caused by a conflict with the on board audio controller on your new Nvidia card and your motherboard's audio controller. You can try the following uninstall method which will fully disable the audio controller and should help eliminate the issues you are experiencing.
1. In the Control Panel, go into the Device Manager. Expand "Display Adapers" and right click on the 400/500/600/700 series card, and select "Properties". In the tab named General, look for the entry called "Location". It should read, for example, "PCI_Bus_1, device 0, function_0". If using multiple cards please check and note each listing.
2. Go under "System Devices" and scroll down the list until you see "High Definition Audio Device". There should be at least two entries, possibly more if you have multiple video cards or a sound card. Check them under "Properties" as you did with the video card to see which one matches your the PCI Bus location. Disable (not uninstall) the one that matches your video card.
3. Look under "Sound Devices" and it should no longer list the Nvidia High Definition Audio Controller (this step might or might not require a restart).
After restarting, a clean install of the Nvidia drivers is highly recommended. This can be done by running the latest driver package, choosing "Custom installation", and checking the box labeled "Perform A Clean Install". This will will remove the previous drivers and re-install them rather than over-writing the existing drivers.