Definitely having a strange issue.
Noise-wise, the PC was all but silent under load. Then I installed a new case fan in the rear, a case fan in the front that is above the other front case fan, and I also installed an HDD.
Now, I'm noticing a high pitched whine or buzzing when I play games. The noise switches pitch depending on different things happening in the game, such as when I'm clicking through the menus. Also, the pitch will sometimes immediately go silent while the game freezes for half a second then start up again as soon as it unfreezes.
I thought this was an HDD issue so I moved the game to my SSD and I still hear it.
Any ideas? This will drive me crazy. I was so happy with how silent it was before this.