CPU coolers and Fans

Fans

• As a general rule, bigger fans should be quieter. Thus it's best to take the biggest available fan that fits into your case / CPU cooler. Then you can check RPM and decibel (noise) levels.
• When trying to reduce the noise of the PC, you have to take into account ALL fans that will be present. If you forget some, you may end up with a poor result. For instance, in addition to the usual CPU cooler fan and additional case fans, the PSU (Power Supply Unit) has a fan. The motherboard can also have a VRM heatsink and fan. I am not sure what exactly is the VRM heatsink fan but with the Asus - ROG Strix Z590-I motherboard, this fan could go up to 10K RPM and was responsible for 95% of the noise of the computer when it triggered. Hopefully, this fan could be disabled (or at least controlled) in the BIOS so the issue was solved in this case.
• Fans should be connected to the motherboard. The newer standard is to use 4 pin connectors with PWM (Pulse Width Modulation).
• Motherboards may not have enough fan headers. There are cables like the Noctua NA-SYC2 that will solve this issue though. You can also use the pump header for a fan if you only use a CPU cooler fan - it will work, although some fan headers do not allow for correct control of the fans. With the Asus - ROG Strix Z590-I motherboard for instance, a fan connected to the AIO pump fan header will apparently always run at full speed.
• When connecting the fans / building the PC, note what fan is connected to which motherboard header. It can be useful for troubleshooting / fan configuration in the BIOS.

CPU coolers

• A bigger CPU cooler is better but be very careful of the dimensions of your cooler as it needs to fit in your case. A compatibility site like Pangoly should always be used before buying.