The sound is likely from the inductors in the power supply charging circuit, it is particularly noticeable when the CPU is under load, like scrolling through pages as you say. I noticed this sound with my own Zenbook and I think it only occurs when the laptop is plugged in and experiencing load, it is not there when the laptop is running on battery even if you force the CPU at 100%. If you go into Windows power options and edit the performance plan, go into advanced settings and set the Maximum processor state to 90% or some value when the buzzing stops. The value set here is the turbo boost ratio, if set to 100% on my Zenbook that equates to 4.2 GHz max dynamic clock which is a bit over kill, but makes the windows experience seamless. I prefer a balance of speed but also no buzzing sounds, so setting the cap at 90% or so, seems to do it for me.
If your issue is outside of the scenario I have mentioned, there could be a fault with your laptop in which case you should probably look at sending it back for inspection.
