I think the nvidia sound is just a bypass thru the card for screens with speakers on them. Im sure you updated the Realtek drivers. You could try and uninstall all parts of the Realtek, reboot and reload only the latest driver. What motherboard are you using? Some motherboard manufacturers have audio drivers and codecs in their chipset driver package. That might conflict if you use drivers from the realtek site. Double check in windows sound that the onboard realtek audio is set to default. Mine had two realtek audio listed in the settings and both worked but one had cracking and popping from time to time and the other did not.