Newest version of Graphics driver is missing HD Audio driver. Version 188.8.131.5294 has it, but 184.108.40.20629 is missing it altogether. Troubleshooted this quite a bit so if anyone is having problems then this might be the cause.
This appears to be a habit of Intel:
I was able to manually install the latest Intel® Display Audio driver (10.25.0.9) from by extracting the .zip version of 220.127.116.1129:
https://downloadcenter.intel.com/download/27894/Intel-Graphics-Driver-for-Windows-10 Download Intel® Graphics Driver for Windows® 10
It looks like Intel has sort-of-solved the problem & removed the .exe version of 18.104.22.16829 altogether. Now only the .zip version remains, which is unfortunate for customers that prefer the self-installing .exe driver updates.