How is transformer noise caused?

Specifically, the transformer noise has three sound sources, one is the core, the second is the winding, and the third is the cooler, that is, the sum of the noise caused by the no-load, load and cooling system. The reason for the noise of the iron core is that under the action of the alternating magnetic field of the silicon steel sheet of the iron core, a small change will occur, namely magnetostriction. Magnetostriction causes the iron core to vibrate periodically with the change of excitation frequency, and the core magnetostriction deformation is caused by the electromagnetic force in the winding, oil tank and magnetic shield. The vibration of the winding is caused by the electromagnetic force generated in the current winding, and the leakage magnetic field can also make the structural parts vibrate. The electromagnetic noise is caused by the longitudinal vibration of the core laminates induced by the magnetic field. The vibration amplitude is related to the magnetic flux density of the core laminates and the magnetic properties of the core materials, but has little relationship with the load current. The electromagnetic force (and vibration amplitude) is proportional to the square of the current, while the emitted sound power is proportional to the square of the vibration amplitude.