Wherefore is my Laptop's battery charger is devising a loud buzzing noise?

Hi, my laptop's battery charger has been making this loud buzzing noise constantly when it's plugged into my laptop. Also bizarrely enough, when I enter my headphones I can hear the buzzing noise from them also . When I unplug the battery charger's line all the rumpus Michigan. What is the problem and what can I do work out it?