I'm having the same issue. I have an ASUS ROG Strix Z370-E motherboard with an 8700k and was noticing CPU usage was 20%+ at idle. I ended up narrowing it down to the Lighting Service... Service. After restarting the service, it would go down to a more level, but soon spike back up. Disabling it completely would get my idle loads down to 0-1%. For a completely unrelated reason, I ended up with a fresh install of Windows 10 with the same issue right off the bat. I now have the Lighting Service disabled. Not sure if this matters or not, but I also have G.Skill Trident Z RGB memory and a Cooler Master air cooler with addressable RGB. I haven't done any testing beyond the fresh install and determining what my usage cause was.