annoying buzz

Hello everyone, Today I casually using my PC when I heard a low-pitch (not high-pitch like coil whine) whining noise coming from my case that sounds like fluorescent tube, I don't really know what's causing it, but it's very annoying and it doesn't seem normal, it happens while PC is idle...

I built a new PC and also need to replace my 1tb Western Digital Black because I am running out of room on it. I purchased a 2tb Black because I had such good luck with the 1tb, but that was a MISTAKE. Upon first start up and first shutdown, I experienced the same issue so many others...