Bigbruin.com has posted a review on the HEC Group Zephyr 650W ATX Power Supply

Noise is always a concern, and I am happy to say that even with the 120mm and 80mm fan in the Zephyr 650W, the system remains virtually silent. You have to pay close attention to notice the thermally controlled changes in fan speed, as you simply can not hear them even when they are operating at full speed.

HEC Group Zephyr 650W ATX Power Supply Review