I have 2 DDC pumps, 1x10W for my cpu loop and 1x18W for my gpus loop, I'm running them at 10V and I cannot hear anything coming from the pumps, even at 12V you almost cannot hear them, my head is 80cm far from my computer the only noise I can hear from my pc is the fans at 1200rpm or more and sometimes the HDDs clicking.
Also I'm using the EK heatsink on both pumps, I have temperature sensors on both heatsinks and usually they don't go over 32C.
Be careful if you are going to use the heatsink with tops or attached to revervoir, sometimes you will need to replace the screws that comes with them, so make sure you get the right size.