This is expected behaviour and it happens on my RX 480 and my Radeon Pro Duo. Even at idle Aero will use GPU resources and so will using a web browser and watching online video. If you disable hardware acceleration in the web browser, the CPU will perform video playback and this will lower your clocks.
A note about power, memory power consumption at 2000Mhz is barely any different than at 300Mhz so it is nothing to worry about.
If you enable Power Efficiency and compatibility mode, you should find the GPU clocks will fluctuate less at idle and when using a web browser to playback video.
doesnt really help me.
my old nvidia 770 clocked at 135mhz on desktop and in videos ~408 sometimes ~700mhz(short peak), never its full clock thats how you save energy same goes for RAM.
i dont mind a gpu clocking up while a video is on the screen but even a 4k video is only 25% load with 300mhz, so there is really no need to set up a higher(full) clockspeed.
i tried power efficiency result: even in games the gpu ran between 300 and 1290mhz, frametimes were horrible. but this could be linked with the bad profile management from the driver. driver sees my installed games, makes profile but doesnt load it when i start a game. i have to add the .exe by myself and then start from the driver. at this point almost every game will start with its own profile.
i really love wattman it is an excellent tool but still beta, crashes frequently