Check CPU mounting
Ensure that the pump has been fastened correctly, with the screws tightened fully. Screws should be tightened in a crisscross pattern, as shown in the installation guide.
Check thermal paste
Use the correct amount of thermal paste. The CPU should be fully covered with the thinnest possible layer. Both failure to completely cover the heat generating areas and applying an excessively thick thermal paste layer will result in higher temperatures. Do not re-use thermal paste if dismounting and re-mounting the cooler.
Check pump and fans
Ensure that both pump and the fans runt at full speed (minimum 9V on pump). Fan speed controls may have been enabled on your motherboard, please refer to your motherboard settings.
Check the system for air
After opening the system, or after prolonged use (2+ years), ensure that there is sufficient liquid in the system by shaking the radiator. The radiator should be nearly silent when shaken. Excessive air in the system will also make the pump go faster and making the system more noisy. Refilling the system will decrease noise.