This isn't super scientific, I just pointed my iPhone at my computer. Ambient room with computer on but not running KeyShot is about 43 decibels, and with my workstation on full CPU usage it goes up to about 46 decibels.
I really think your case and cooling are going to make the biggest difference here, not the specific CPU. I have a liquid cooled setup + fans on 4/6 surfaces so it's probably a bit louder than just an air cooled system.