If you have seen professional tennis players on the court, you have definitely heard the grunting they do when they hit the balls. This happens because they hit the balls during their exhale. The harder they hit, the louder the exhale and sometimes it sounds as if they are screaming. By the way, Maria Sharapova is the loudest tennis player in the world: she plays at a volume of 101 dB. For perspective: an underground train is only 100 dB.