I don't have one of these switches, so I don't have any specific advice. The manufacturer chose that specific fan to meet their performance requirements. Those requirements presumably include the ability to continue to operate with a single failed fan (so the cooling is probably over-engineered a bit) but also the expectation that the switch would operate in a datacenter (a more controlled environment than the average home). There's no "magic bullet" to get a quieter fan with identical performance specs - no fan manufacturer decides "we want to make a noisy fan". Quieting things down requires a fan with different performance specs - generally, larger fans and lower RPMs are quieter. If you're using the stock fan cutouts, then you have limited choices.
If I had one of these switches and had to make it quieter, I'd probably have some adapters 3D printed with a taper (a squared-off cone) so I could mount larger fans outside the case using the existing cutouts. That would allow me to move the same amount of air with a larger fan at a slower speed. That's the same idea as the original "
TURBO-COOL" from PC Power & Cooling (then PC Cooling - Power came later). Of course, it would interfere with mounting equipment directly above or below it in a rack, but so does the "cut big holes in the top and put fans on them" solution.