I was having the same issue. Thought it was a hardware problem after talking to Asus and adjusted the bios to shut off the RGB at shutdown. However, after digging into it some more, I discovered that the issues was related to the Shutdown Effect in Armoury Crate. I had been using the Starry Night effect when the pc was on and apparently set the same for the Shutdown Effect. When I changed the Shutdown Effect to static, the flickering stopped. Turning off the Shutdown Effect will also shut the RGB off completely at shutdown.