M8H for a few months now. Sound pops on every startup and every now and again when the audio channels open. Apart from that, this board rocks, and the sound is great, but yes it is very annoying to hear that pop on startup. I wish someone from ASUS would elaborate on this further.
6700K, 1302 BIOS and I have all ASUS drivers installed with sonic and AI suit on WIN10. The rest of the HW is irrelevant for this sound pop issue. Since some people have the issue and some don't, I believe it would come down to a software problem. C'mon ASUS, take a bite at this and tell us where the problem comes from.