Buzzing sound from back of ipad

Every time i put my ear in the back of my ipad i can hear buzzing sound if my ipad is open, the buzzing stops if i turn it off. It also gets slightly loud if i tap. Is this normal? You can only hear it if your ears are touching the back of the ipad. In the center to the charging port, i cant hear in the top side of my ipad or in the camera side of the ipad. Is this normal?