What's obnoxious is screaming, which I've only heard from WTA players, though, I'm sure there are others. And they tend to do it on every shot. How come nobody had to scream/grunt in the old days?
There actually was grunting in the old days.
Jimmy Connors, in the
early 1970s, was more pronounced than players that came before him. In the 1980s,
Andre Agassi would often grunt on big shots. One of the first of the very high-decibel grunters was
Monica Seles (who turned pro in the late 80s).
Seles probably hit the ball harder than any female pro player previously. After complaints at Wimbledon in '92, she was asked to stifle her grunting in the finals. Seles, who was very dominant in both '91 and '92, lost decisively to Graf in that Wimbledon final. After that loss, Seles vowed that she would never again be pressured to suppress her grunting -- she felt that it destroyed her breathing, timing and confidence.
Note that many of the loudest grunters came out of Nick B's academy -- the list includes Larcher de Brito, Seles, Sharapova, Agassi, and the Williams sisters. It has been suggested that grunting was encouraged at Nick's academy as a tactic used to distract opponents. If the grunt is "voiced" during ball contact, it is possible that it can also obscure the sound of the ball contact. The sound of the ball contact can often provide an opponent with very early cues to the nature of the contact (spin, speed, and how clean the contact is).