I just noticed something interesting. When I charge my laptop, touch the laptop with one hand and stroke a metal surface with the other hand, this metal surface vibrates noticeably (also audibly). If one of the 3 things is not there, then this effect is not there. Can anyone explain why this happens?
So that shouldn't be noticeable for now.
Your laptop or its charging module should actually be 'potential-free', i.e. Not generate any voltage (and therefore no noticeable vibrations of the mains frequency) between the laptop and the so-called 'earth', here the metal surface.
However, if this is the case, the insulation (electrical isolation) of your power supply is very likely to be defective.
Better replace the power supply!
Does your laptop still have a vibrating hard drive, the noise / vibrations of which you transmit through your bones?
Or is the power supply (which is also necessary) right next to it on the table, the parts vibrate minimally.
It could also be capacitors that vibrate due to the charging current. You will probably only hear the noises because the metal plate is quite large and maybe coincidentally resonates in the resonance range (100Hz or integer divisors / multiples).
Other electronic components can also resonate. I still remember an amplifier from the 80s, which you could listen to quietly without a loudspeaker.
There are also metal surfaces that always feel like there's tension on them. Brushed stainless steel or something…
Simply measure voltage against PE.
