There are blade design differences bearing differences motor differences etc. There are 40mm fans ranging from 10 dB to 100 dB. Again if someone wants to bother and look at what fan and what specs. they currently are, they can then source their own "better" or "quieter" equivalent.
A fan spinning at 6000~9000 rpm can never be quiet, no matter the bearing or blade design. It's impossible. At this level, you don't hear any noise from the ball bearing, you just hear the airflow. At this fan speeds, you will NEVER achieve laminar flow.
The bearing
does matter if you look for fans spinning at 300~500 rpm. Then you even prefer a sleeve bearing over ball bearing, because sleeve bearing is more quiet. Again, at this level you only hear the mechanics of the fan, not the actual airflow. But for fans with many thousand rpm, ball bearing is the only option and turbulent airflow will always be noisy.
If you want a quiet SP10, go for watercooling.