Corsair H115i fans
Corsair H115i fans
Honestly, the concern isn't about the pump itself but rather the fans that come with the coolers. Just opt for a low dB fan model to replace them. I own an H100i with two Cougar fans installed, and I haven't heard any noise from either the pump or the fans.
I swap out stock fans in any sealed cooling setup. Usually I pick Cougar models because they're extremely quiet (18-20dB) and move a lot of air (70-90). Noctua works too, but they're not as silent and cost more. It's all about personal taste.
The Kraken is just as noisy with stock fans. But Corsair fans are definitely the loudest—like jet engines.
You have the option to adjust the fans to lower the noise level, though the pump will produce some sound. This applies to all AIO water coolers, including the Kraken X61.
The difference in performance between an NH-D15 and H115 is minimal.
Honestly, the concern isn't about the pump itself but rather the fans that come with the coolers. Just opt for a low dB fan model to replace them. I own an H100i with two Cougar fans installed, and I haven't heard any noise from either the pump or the fans.