electric shock from my iphone 12

When im charging my mobile using a case there is a small electric shock comes from the aluminium part of the back cameras.. I tried removing my case and charged my phone but at that time there is no electric shock coming.. its was a kind of strange thing.. i tried it using many case made of different material and i charged but still small amount of electric shock is coming.. what is that?? is anybody affecting the same issue?? some people may not notice it..