Sometimes there are instances where a liquid cooler can make a gurgling or other unusual sounds. This is typically caused by air stuck in the cooler that needs to be circulated through the built-in traps on the radiator. Any air bubbles tend to go away quickly on their own as the coolant flows through the cooler. In some cases, it may be necessary to physically manipulate the radiator to free any stubborn air bubbles.
This can be done in two different ways.
1) Unmount the radiator if it is installed in a PC case then gently shake it to loosen any air bubbles.
2) Lay the radiator or system on its side and let it run for until the sound goes away. It can take about 15 minutes before the sounds go away.
These methods are also recommended if drastically high temperatures suddenly occur.