I need to confirm something based on my observations only.
Yesterday my local store was selling an opened PS4 Pro ( someone it seems got it as a gift and he played it and decided to sell it )
anyway so I borrowed the system. and hooked them up both at the same time. did game transfer and played COD MW2 on both my accounts ( I have 2 accounts ).
I made sure both IDs on the same team and started playing on both IDs. I noticed that the one I got from the store actually IS louder. I mean, both fans kick into higher gear during match making. but the one from the store fan it self is actually louder than the one I have. not by much, but you can actually both hear them.
I didn't open any of the systems ( even the top cover as its wasn't mine to confirm if they share the same numbers of blade or same fan type. ) but both of them are recently new systems, I highly doubt its related to dust.
Also, if some people have a fan noise this level
https://www.youtube.com/watch?v=UrSMGWGqhyw
then please return it that's not normal lol