The produced noise of each CPU cooler depends on the design and material of the fan ant it is generally proportional to its rotation speed. The Noise tests, proved to be rather difficult since you can't just post a number and be sure that it's accurate. There are many factors that can increase/lower the produced noise of a CPU cooler, but anyway all displayed models were tested in exactly the same conditions. Keeping the rotation speeds at full throttle gives us the best possible performance. However it also increases noise.

Looking at the test results, the ThermalRight SI-128SE was very silent with 50dB at full rotating fan speed.

Lowering the rotation speed down to a minimum does reduce the produced noise. Again ThermalRight SI-128SE rocks this test with only 45dB noise.