Connecting 3phase motor to FC
A VFD may work with PWM. These step functions have a broad frequency width, and in case of a 3-phase motor, most probably the current is in the 2 or 3 digits Ampere range at certain times like starting under load etc.
That means, the VFD could emit relatively much power (like a short wave sender does intentionally), if the length of the cable to the motor is - by conincidence - matching certain wavelength conditions like an antenna.  Since the frequency bandwidth of PWM is rather wide, the chance to emit some tens, hundreds or even more milliwatt in certain frequency ranges is high.