I know this is a while ago but I am having the exact same issues, but only since the latest patch. I also have a realtek onboard card. I am going to order a DAC to see if that changes things.
I have tried the following:
Reinstall, and verify files on steam.
Disable Steam Overlay
Disable Hardware Sound and Mouse in the options.
Change sound bitrates in windows from 24 bit and 16 bit between 44khz and 192kHz
Whitelist BB in bitdefender
Updated NVIDIA drivers for GTX 1080
