Some first order guesses: -Have lots of blades on the same rotor so the assembly can turn slower -Put the tail rotor inside a shroud -Having a smaller rotor mi

Some first order guesses: -Have lots of blades on the same rotor so the assembly can turn slower -Put the tail rotor inside a shroud -Having a smaller rotor might help, since the spread in air speed across the length will have less variation (less sure if this would help) -Turbine engines can be pretty loud, I'm guessing the same is true of other powertrain components. Maybe put the loudest stuff on the roof.