MiSTerAddons.com put several of the most popular 40mm fans for MiSTer head to head to find out which type is the quietest and keeps the DE10-nano the coolest. His test methods are scientific in that they take the ambient temperature and room noise into account, and he’s taken safeguards to standardize variables that may have skewed the results.

The winner may not necessarily be the fan that you would have expected.

https://misteraddons.com/40mm-fan-shootout-part-1-noise/