It's a lot easier to build a PC from the ground up to be quiet and some cases are much much better than others, and have damping for sound etc.
I spent a lot of time researching and attempting to quieten an old coolermaster case I had in the early 2000's, failed miserably, brought an antec P180, massive difference, i've now moved onto a fractal R4, only a bit quieter but easier to work work.