Hi Pete,
Get together with Peter and he'll show you how quiet a Genesis is, at least at normal speed. The motor switching noise gets louder at high power levels, but so does the water flow past your ears at that speed, which also creates noise. What you will likely find more important than noise, is how easy or difficult it is to control the speed of each DPV while diving. That's where the Genesis shines.
As for the technical answer to the questions, there are a few of things that we do to reduce motor noise, which mainly has to do with winding configuration. Most of the noise comes from the motor controller switching with a trapezoidal control, which is a bit noisier, but more efficient than sinusoidal control. High frequency switching is also a bit quieter, but also less efficient, so there has to be a balance point that each design tries to achieve. Since range, size and weight are generally more important to people than noise, we opted for a trapezoidal control for increased efficiency. Very little noise comes from the propeller on most DPVs, unless it is hitting the shroud or it is a small diameter propeller, spun extremely fast.
At normal cruising speeds, the Genesis is very quiet. At high power, you will hear the motor controller switching. When you hear noise on the numerous online videos of different DPVs it usually depends on whether the camera is on the diver or hard mounted to the DPV with any sounds vibrations conducting directly to the camera housing. Video editing software also can reduce or amplify the sound, so videos of a DPV are not a good gauge of noise.
Cheers,
Jon