Not very easily. Firstly, the power involved in these systems is massive, making any inductor or capacitor you put in very expensive (and bulky). Secondly, filt

Not very easily. Firstly, the power involved in these systems is massive, making any inductor or capacitor you put in very expensive (and bulky). Secondly, filtering it out may reduce the sound, but still will have some part of the circuit switching at that frequency, and with the power involved, some part of the inductor will see that and vibrate accordingly. Modern power electronics generally avoids this problem primarily by pushing the switching frequency higher than human hearing (which also has other advantages, like reducing the inductance and capacitance involved). Generally the higher-power the device, the physically bigger it is, and the slower you can switch it without melting it, so bigger systems are stuck at lower frequencies (this is something that's improving as technology develops: so there's the other factor that most train stock is quite old and the designs older still, meaning they switch even slower than your new laptop, even taking everything else into account).