Why do fluctuations occur when I run the palm of my hand over my notebook?

Whenever I connect my laptop to the battery to charge it and stroke the closed screen with the palm of my hand, there are fluctuations or vibrations like sound waves, as if one were being electrocuted.

What is it and why is it so?

This can happen if the screen or the housing is made of metal and the power plug has only two contacts (no protective contact).

These are interference suppression components in the power supply unit, which forward a tiny part of the mains voltage to the low-voltage output. Then you can feel a "current" tingling when you stroke the metal housing of the computer.

But that is not dangerous.