Heh. If I plug an iPad charger in the "wrong way" (symmetric EU socket), I observe massive interference/hum via the 3.5mm audio jack. The hum disappears if I rotate the plug, or touch the metal backplate of the iPad.
I have the exact same issue with a MacBook (2015). As soon as I plug in the audio jack, I will hear background noise, except if I touch the aluminium body.
I solved the problem by replacing the default short connector to the socket with a desktop-like long power cable, that unlike the short one has a ground connection.
