Due to the magnetic field that builds up inside an electric motor,
and the fact that this field oscillates in time, the Maxwell's equation predict a variable
electric field as a consequence; this will in turn cause interference to
nearby radio equipments (TVs, computers, cell phones, etc.)
If the motor has an adequate metallic shielding that adverse effect would be
greatly reduced, thus the term non-interference.
Other methods are also available, as trying to confine the magnetic field to a very
The Maxwell's equations are the ground for predicting all (non quantistic) electromagnetic phenomena; Maxwell published his work in 1862 and they are still perfectly valid!