We all know that electric motors and electric cars are quiet compared to internal combustion engines and cars. This is one of the first things one would notice when switching to electric. The car is turned on and quiet, without vibrations. You can also talk without raising your voice.
However, because there is no noise of the engine, after a longer time you start to adjust and recognize tons of other things - parts that are not exactly aligned, tires, high-frequency noise from the motor/power electronics or some fans. To make electric cars quiet without those other sounds, manufacturers need to spend some effort.
Autogefühl noted in one of the latest reviews of the Audi e-tron that car is very quiet, even at high speeds (quieter than Tesla, for example). When we dig deeper into press materials we can spot there is a hell a lot of acoustic insulation in e-tron.
Audi tries to reduce the noise at the source - like on the motors or wheels - as well as isolate the passenger compartment from the rest of the car:
Wheel well liner insulation, exterior
Microfiber fleece parts to fill cavities
Motor mount / rubber mount
► Motor connection to the subframe
► Second decoupling level
Subframe / rubber mount
► Subframe connection to body
► First decoupling level
Encapsulation of electric motor
► Open-pore PU foam
► Absorption of motor noise
Motor support made from aluminum