I have an SFF Dell Optiplex I bought for $100 many years ago that’s still my main “homelab” machine. It’s fairly quiet besides the two 12TB spinning hard drives inside but the fan isn’t noticing.

A rack mount server would be out of the question as I live in a small condo, both for size and noise.

When my G3 (newer version of parent's machine) is booting up all of the VMs it's running it can get kind of noisy but it settles down quickly to basically silent.

Barely audible, you have to have your ear <1ft from it to hear the hum.