Where do you live? You should be able to take a measurement of the current fan and look on Amazon or EBay. There are much quieter fans out there (I have replaced fans on a lot of gear but not on my SQ, yet) and in some cases, I put a diode in-line with the DC-hot wire and reduce the RPMs of those fans. YMMV on the safety of doing this but I will say that I have never had a problem caused by a reduced RPM fan in any of the many pieces I have done this to.
I do hear the fans in my SQ6 and it does bug me a bit that there are quieter fans on the market that could replace the sorta-noisy fans installed in the SQ line. I guess that every dollar counts in the manufacturing world but if you’re gonna say that your mixing panel is appropriate to be used in a studio control room, and everyone can hear the fans, you might reexamine either your builds or your marketing.
D.