I've got one of these in my HTPC and it's inaudible.
I do think that it needs the bigger rad to be efficient though as the heat generated by the pump is right on top of the CPU block. When I had mine running to check the loop for leaks it felt warm to the touch.
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I have a question: how warm do you mean? I'm running leak test now and my pump/block is pretty hot to me - It is running in the loop: pump/block - radiator - t line with fillport - pump/block. Nothing is attached, I mean it is not cooling anything, computer is running next to it giving only a power to the pump, but pump is not sitting on cpu. Radiator doesn't have fans on it - maybe that is the case?
Top of the pump is very hot, I can barely touch it! Sth is not right. I took all air out of the loop, at the beggining I thought that was the reason for running so hot, but now, when there is no air (I think...) in the loop and pump became silent it is still running very hot. Pump is generating 10W of heat, I think that 2x120 radiator should take that heat out, even without fans, right?