I have a NZXT H700i. Now if I compare my friends pc in the same tower with a after market cooler. When he turns it on I had to double check I pressed power cos it was silent. In mine. I hear a tiny noise. When at full speed. I can hear it. But it isn’t loud. In fact my old AIO was louder. So I definitely know what a good quality silent cooler is like. And I’ll upgrade soon just so it runs cooler than the stock one. But I just can’t understand the loudness thing.
Maybe you just got lucky... or perhaps double-check that you aren't accidentally under-volting :)