Final answer:
An AC magnet may hum excessively due to improper alignment, foreign matter between contact surfaces, and loose laminations. An AC magnet may hum excessively due to All of the above.
Step-by-step explanation:
Improper alignment, foreign matter between contact surfaces, and loose laminations can all contribute to excessive humming in an AC magnet. Improper alignment can cause the magnet to vibrate and produce a humming sound. Foreign matter between the contact surfaces can create friction and cause the magnet to vibrate, resulting in humming. Loose laminations can cause the magnet to vibrate and produce noise. Therefore, all of these factors can contribute to excessive humming.