SPCR

I purchased this model after reading SPCR's review of the 720w model. Upon powering up my new build for the first time, it sounded significantly louder than one might assume from the review. Subjectively, it sounded louder than the new Acer pre-built small form factor desktop I tried a few days ago. I used my iPhone to run a decibel app to test this PSU against my Seasonic. The following are measured on the surface of each PSU:

CoolerMaster Silent Pro M2 620w: +27dB above ambient noise level
Seasonic SS-430HB: +14dB above ambient noise level

Subjectively, the CoolerMaster would be "loud / somewhat loud" and the Seasonic would be "quiet / very quiet" in my opinion.

I'm not sure if I did something wrong, but I didn't see any settings that could alter the CoolerMaster's fan speed. I think I'll return the unit.

What's the system setup, is the power supply getting fresh air?
Just curious since that's very relevant to the resultsing noise.

It is a good idea when buying any power supply to check if there is a fan profile available from the manufacturer, this will let you know fairly precisely how the fan will behave at idle and under load for the particular model concerned. Sometimes PSUs in the same model range use the same fan profile, sometimes they are different. In this case the 720w has a different fan profile from the 620w. Looking at the two profiles it seems to me that the one for the 620w is less quiet, with the minimum fan speed being higher than it is for the 720w and the 620w profile also runs the fan at higher speeds as load increases. So yes, the 620w would be noisier than the 720w.

From the Cooler Master website, this is the page for the 720w M2 and this is the one for the 620w. The fan profile is found part-way down the page under 'More highlights'.