If you look at computer case fans, you can find commercial examples dating back to at least 2012 that are specifically meant to curb noise: https://www.overclo

If you look at computer case fans, you can find commercial examples dating back to at least 2012 that are specifically meant to curb noise: https://www.overclock.net/threads/noiseblocker-nb-eloop-120mm-bionic-loop-propeller-fans.1289723/ https://www.overclock.net/threads/noiseblocker-nb-eloop-120m...