OK, so you have the new drivers downloaded in your Downloads folder, right?
Uninstall all the Nvidia drivers in Programs and Features which you can find in the Settings, or by a shortcut by right-clicking the Windows logo down left and left-clicking "Programs and Features". When you've uninstalled them, choose the same shortcut and left-click "Device Manager". There you should find your Sound devices. Disable the Nvidia High Definition sound device (right click for a shortcut) but leave the Realtek High Def. Audio as is.
After having done that, reinstall the drivers from your Downloads folder, this time unchecking those I mentioned. And yes, check the Clean install box.
If by chance you would need to make sure all of your previous drivers are gone, there's third party programs for wiping them off. But that's another story.