There are blade designs specifically tuned to reduce noise. This is a recent new design. “Toroidal propellers: A noise-killing game changer in air and water”

There are blade designs specifically tuned to reduce noise. This is a recent new design. “Toroidal propellers: A noise-killing game changer in air and water” https://newatlas.com/aircraft/toroidal-quiet-propellers/ https://newatlas.com/aircraft/toroidal-quiet-propellers/