By Martyn Herman

LONDON (Reuters) - Wailing Belarusian Victoria Azarenka has already ratcheted up the decibel levels at Wimbledon this year and the 21-year-old fourth seed is unlikely to turn down the volume despite criticism from the All England Club.

Relative silenced reigned over the All England Club on Tuesday when the fourth seed was not required to return to Court Two to finish off her match against Magdalena Rybarikova after the Slovak pulled out.

Earplugs, as well as umbrellas, could be needed later on Wednesday, though, when Azarenka was scheduled to lead the chorus in second-round action on Court 12 against Iveta Benesova.

She was measured at 95 decibels on Monday, still a little quieter than the 105 decibel shrieks emitted by Russian Maria Sharapova in 2009 but still loud enough to echo across the outside courts.

Azarenka is not alone in making a racket when she hits the ball and five-times champion Venus Williams was cranking up the volume under the Center Court roof against Japanese veteran Kimiko Date-Krumm on Wednesday.

However, it is the prolonged nature of her grunt and the fact that she is still in full cry by the time the ball has reached her opponent's strings, that singles her out.

All England Club chief executive Ian Ritchie is among a growing band of people getting fed up with the incessant soundtrack to women's tennis, but Azarenka insists that she is doing nothing wrong.

"I can't change it, it's part of my breathing system and it's just natural and something I've done since I was a kid," she told Reuters in the build-up to Wimbledon. "I don't want to change something that comes natural.

"You can get upset about a lot of things on a tennis court," Azarenka added, when asked if she felt her grunting was unfair to opponents. "Some players shake their rackets in front of your face but it doesn't get mentioned much.

"People have their own tricks. Sometimes they call the trainer 20 times. Grunting is part of the game.

"I don't do it to annoy people and if you hear me practice I also do it then too."

Whatever she says, Wimbledon chief Ritchie's patience appears to be wearing a bit thin, even if there is very little he can do unless the International Tennis Federation (ITF) and women's tours decide to act.

"We have discussed it with the tours and we believe it is helpful to reduce the amount of grunting," Ritchie was quoted as saying in the Daily Telegraph on Wednesday.

"We have made our views clear and we would like to hear less of it."

(Editing by Ed Osmond)