Dell XPS 15 9570 loud buzzing noises especially when plugged into a power source

I have been using this XPS 15 9570 for about one year, and this problem happened three weeks ago. A loud buzzing noise emits from the inside and I cannot tell where exactly it comes from. I have run several diagnostic tests on the official website and via SupportAssist, and I installed all the necessary updates. The results show that everything is normal. However, the noise will continue if plugged into a power source and never stops unless I shut it down.