why is there noise in adapter?

When the AC 220V is transformed by the transformer and converted to DC through the rectifier, there is consumption here, and these consumptions are converted into heat, so it is normal for the power adapter to heat up. The transformer is made of silicon steel sheet. When the transformer is energized, a magnetic flux is generated. The magnetic flux will cause a force between the silicon steel sheets to generate a click sound, but this is normal.