What causes the humming sound in transformers?

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Transformers hum primarily due to vibrations in the iron core, which are caused by the alternating current (AC) flowing through the coils. This AC induces changing magnetic flux, leading to magnetostriction in the iron, where the material's dimensions change in response to the magnetic field. The frequency of the hum is typically 120 Hz in regions with a 60 Hz power supply, or 100 Hz in areas with a 50 Hz supply. The phenomenon occurs when the magnetic excitation exceeds approximately 1 Tesla, causing the core to vibrate twice per cycle. Understanding these mechanics clarifies the source of the humming sound in transformers.
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Why do transformers hum? Is it the iron core vibrating & if it is what is it that makes it vibrate? Is it the little atomic magnetics in the iron changing directions with the ac? Can anyone enlighten me?
 
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Basically I think you are right,the coils carry a.c.and this results in the core going through many magnetic cycles per second.The changing magnetic flux then results in vibrations.
 
Magnetostriction in the iron causes the iron laminations to change dimension when the excitation exceeds about 1 Tesla. Magnetostriction occurs twice per cycle, so the hum is 120 Hz (or 100 Hz) depending on where you live.
 

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