Answer

It is a common phenomenon due to the resonance from electric components especially inside high-performance PCs or laptops. The buzz emitted due to the resonance from MLCC on the mainboard when CPU is rapidly switching between different C-states.

Not every human would hear this resonance sound as the volume is small and it depends on the volume of the ambient sound in your environment. On top of that, this phenomenon has been confirmed not inducing any safety issue to the laptop.

To ease this problem, suggest to disable "CPU C states" in the BIOS (only available on some models).

Reference