Some years ago when I still had my 2009 Macbook Pro I noticed that if:

- The laptop was charging

- I was touching the laptop with one hand, and either (my memory is fuzzy on the details by now but it was one of these two circumstances):

- A friend was touching me on the side of the forehead with one hand and touching a crack on the wall with the other hand

OR

- I was the one touching the crack on the wall with my other hand.

Again, I don’t remember which of these last two. BUT I remember the result: I would see banding with my eyes (very similar to what you see with cameras when their shutter doesn’t sync with AC power).

Now, our eyes don’t have shutters so I have no idea what was going on but I saw it.

I’ve had this issue with all my MacBooks since 2010 with ungrounded chargers (because Apple don’t use grounded plugs for whatever reason although the contact exists on the charger).