Since latest 1903(some reported even earlier) update for Windows 10, I and many others having problems with elevated memory clock on Radeon RX580 and some other Polaris based cards. I have a single AOC 75Hz(native) FreeSync monitor connected via displayport and at this frequency GPU memory clock is raised to maximum of 2000MHz. In this state graphics card temperature is slightly higher and fan is active. Workaround is simple, by reducing refresh rate form 75 to 60Hz(right click on desktop, display settings, advanced display settings, display properties, monitor) memory clocks are back to idle values of 300/300MHz, temperature is back to normal and AMD zero rpm is not compromised. You can still use higher refresh rates in games but the memory clock will not stay an maximum returning to desktop. Drivers from Windows update version 17.1.1 work fine in this regard, but you have to choose between nominal desktop refresh rate of your monitor and new features and optimizations of latest drivers.