Actually, yeah, just to expand on Mack's and my own comment.
There is also a hum from the electrical components themselves (that is, if you ran the launch without a train, you'd still hear some of the noise - albeit likely a lot quieter). Again, this is vibrations caused by the magnetic fields interacting harmonically with the materials within the device. Electric motors with laminated cores will be excited at some natural frequency depending on the pattern of the electricity being supplied to them (hence why the pitch changes as the speed or torque changes). You can often hear a constant "hum" from those big electrical substations dotted around cities - this is the effect of these natural resonances occurring at a constant frequency (50 or 60 Hz depending on your country). It's the same effect within electric motors (linear or rotational).
Should note that the pitch of the noises is often due to frequency of the electrical supply, meaning you excite different modes (stable vibration patterns) and therefore causing different pitches.
On an LIM/LSM, it's this effect of the electrical components, plus the actual vibration of the fins themselves, that cause the 'whoosh' noise.
Equally, on magnetic brake runs (which have no power supply), you're hearing both the vibration of the fins and some natural frequencies of the components due to the electric currents generated by the fins moving past each other. Again, why you hear the noise (although generally quieter) on some brake runs.