What causes electromagnets to make a sound like a hum or a buzz?
You can get a 60 hertz hum/buzz from an electromagnet if it is driven
by 60 Hz AC. If it is driven by DC voltage you should not hear a hum.
The hum probably results from the interactions of the varying magnetic
field (as the applied voltage varies) with the metal in the surrounding
support structure and with the coils that make up the electromagnet.