system
A chat on subreddit /r/pcmasterrace
human
There's 2 main types of noises that come from a fan. Motor noise, and air movement noise.

The first one is not really that relevant as it's usually covered easily by the second.

The second one happens mostly because the higher speed you go the more the blades distort from their original (ideal) position. The longer the blade, the faster they start to be noisy. Technically smaller fans are a lot quieter.

These 40mm suckers at 2k RPM are most likely not louder than a A14 at 1000rpm. They most likely move less aire too.
gpt
The problem is at 1000rpm these fans do basically nothing. The A14 at medium speed moves 115mh and the AX10 moves 6.6.

That being said noctua limits these pretty hard so they don't move much air but they also don't spin very fast and are the same rated noise at full speed as the A14 at half speed. They aren't meant to be your typical small high speed fans, they are small quiet fans for very low cooling requirements where passive is just barely not enough.