Is this anything to be concerned about? I can only hear the sound if I put my ear against the switch. So it's not very loud at all. I checked and re-tightened all the wires as well. It's connected to 9 canned ceiling lights in my living room. 

I hit restart on the switch and I noticed the buzzing stopping while the wifi was disconnected. When it connected to wifi again the buzzing started again. Also when I turn ON the switch the buzzing stops but when I turn it OFF, the buzzing starts again.