It is quite by office standards, but not by soundstudio standards.
The noisiest part - power supply fan.
120mm case fan is variable speed, but even at full speed it is reasonably quite.
Hard drives are mounted on rubber washers, which helps to damp the sound a lot. I am using three quite Seagate Barracudas, and I need to REALLY listen to hear them work.
Hard drives are mounted "sideways" i.e. all hard drive connectors will be facing you when you take side panel of the case off. It is very convenient for installing, connecting and re-connecting the drives.
Like Polaris20 said it is very well built and sturdy. Not a singe sharp edge inside.
Overall it is a very good case. When they finally make reasonably priced REALLY quite power supply unit, it will become a truly quite box.