Loud machines are loud because loud is the easiest. It takes serious analysis and engineering to discover exactly where the noise comes from and/or is amplified

Loud machines are loud because loud is the easiest. It takes serious analysis and engineering to discover exactly where the noise comes from and/or is amplified and fix that. Sometimes you can cut a machine's noise level in half just by tightening a few screws or replacing some raster by a different material, but you don't know which one until you detect where the noise comes from. Your Miele is less noisy because they (and their suppliers) invested lots of engineer hours in making it less noisy, both at the motor level and at the level of the entire vacuum cleaner.