Quiet but not silent
Contrary to what the other reviewer said, I don't find this fan to be silent. That said, I have the computer open on the desk with virtually nothing else making a noise; hidden in a case under a desk it would probably be difficult to hear. I hear a whooshing noise when running it at a moderate speed, or at low RPM it continually starts and stops, which is a little annoying (may be the low-noise adapter, but three other PWM fans I've tried don't do that).Note: I'm nit-picking; it's still pretty good.