I changed the installed 3 OEM fans on the back to a total of 5 Noctua NF-A4x20 PWM fans.
Obviously the 3 on the back pushing air out. On top of that I added 2 fans pulling air in to the PSU side of the chassis where there are small holes in the side panel. Just wanted to be on the safe side since a ServeTheHome review of that switch mentioned that 3 Noctua fans might be too little to handle the 69 W theoretical total load of the switch.
The board has 4 PWM fan headers (so only 3 are used by default), the 2 extra fans are powered with an Y fan adapter using the extra fan header. The Noctua fans spin up reliably and even with 5 of them at full speed compared to 3 by default the noise is much more bearable.
Also, they are not triggering the red fault LED at the switch’s front (read a couple of times that after-market fans could lead to that when modding switches).
But I would never put such a switch next to my desk, I would rather make absurd custom-cooling solutions voiding any warranty before taking that kind of noise permanently.