Wifi Antenna inducing noise into earspeaker

I have a problem with my S8 Plus. Maybe you can help - whether it's normal or not. When I listen with my ear closely to the earspeaker in a silent ambience (even without making a telephone call) I hear some noise that is caused by the Wifi module. It is not there, when I switch Wifi off. It's kind of a very subtle clicking, like an antenna working.