Hey,
You might get some good opinions here but it might also be worth hitting a computer or overclocking forum for deeper knowledge.
Still...What cpu brand/architecture/model do you have? What cooler do you currently have?
Is water an option?
General rule of fans....Bigger-Slower-Quieter.
Also, you're certain it's the CPU fan? You may have PSU fans, case fans, gpu fans etc. It'd be worth finding out for sure.
Was it always noisy? If it's defective and worked fine before you may just need to replace it rather than upgrade.