I would agree with krells, a larger air cooler would be quieter than an aio cooler. Either one of the noctua's or the dark rock pro 3 from bequiet. I'm currently using the drp3 on my overclocked i5 (4.5ghz) and under 100% load I don't hear the fans spin up very hard at all. It's one of if not the quietest fan in my case.
The only time I managed to get the fans spinning hard enough to hear them I had to disable every other case fan and run prime95. With the case lacking any other cooling it finally ramped the cooling fans up. The noctua coolers operate much the same way and chances are the fans will stay on low even when under load making for a very quiet cooler.
No way I know of to get absolutely 'silent' operation from any cooler. Unless maybe you ran a custom water cooling loop with the hoses running to a radiator, fans and pump in another room or something (excessive and unrealistic). You're going to hear the radiator fans, possibly the pump and the coolant flowing through the hoses. You'll also have ambient noises of some sort in the room that may seem extremely quiet but aren't in fact silent.