Which pump was that?
I tried the Corsair H100 and I returned it on the same day as the pump noise was just horrendous (granted, we're talking SPCR standards, but it was absolutely annoying).
The pump in this video is also very annoying to my standards: http://youtu.be/i15O2ZF_W-w
(most probably he has it screwed to the case, amplifying vibration, but still)
The first one was WAY too long ago. It was a small fish tank pump in a metal reservoir. With a VERY slow fan and a huge radiator, I had to get within 6" to even hear the system, and at the time, I was in the country, with little outside sounds!
My current game system uses a Swiftech H20-320 HD Edge, which uses a MCP35X PWM. I just turned off all the fans (love my new AquaComputer Aquaero 5 LT) in the system, stuck my head in the case (it's still open, waiting on a new video card), and all I can hear is either the CD or one of the Harddrives! (I think the CD?) My H20-320 is directly connected to the case, and I am now in the noisy city, so background noise is MUCH higher. Either I got lucky on my pump, or someone got unlucky!
BTW, I have slightly above average hearing, but at my age, I am loosing the higher end. In my 20-30s, I could ALWAYS hear the high voltage on ANY TV (in the tube TV days) when I walked into a room.