The problem with watercooling to me is also the sound of the reservoir.. If I were to consider going for this, I'd probably think of a long trunking and try to leverage the use of my air-con units, at least one of which is going to be on anyway.
To get really low noise at low cost, if all other concerns were not critical, I'd just knock a hole in the wall and put the PC the other side really... too bad most of my connecting walls are to non-useable spaces (e.g. toilets, walkways or roof terrace).
Should be starting the build soon if my friend is up to it. Let's see how it sounds.. if not I can find alternative location to put the PC to get more distance from it.
Though my room is quiet, I think it should not be <10dbA anyway (definitely not during rush hour even though I have triple layered glass). 2-3 low noise fans should be able to achieve <15dbA and if I place it 4-6m away (as an option), it may be inaudible. My old Antec PC was about 23dbA with stock fans and that was abit noisy, but I think liveable with for some gaming performance.