Adding to this: BeQuiet cases. You want that internal sound dampening on all sides of the case (so avoid tempered glass) to get rid of any annoying high-pitched coil whine, not just to silence the drone from fans. I have an overclocked 9700K with a BeQuiet case, the stock BeQuiet fans (which are quiet) plus a Noctua heatsink and extra Noctua case fan. After having adjusted the fan curves it runs cool and is inaudble (from less than 1m away) without headphones.