CPUs do not make noise unless there is something horribly wrong with it to the point of also communicating via light and smoke signals.
Fans are the dominant noise source in most PCs, usually followed by HDDs. You'll have to determine which fan/hdd/whatever is generating the most noise and look at options to mitigate that noise. For fans, the BIOS has fan profile configuration usually offering "Quiet", "Normal" and "Performance" options with Quiet obviously expected to produce the quietest results and Performance having the highest likelihood of being quite noisy.