Maria Sharapova's high-pitched squealing and grunting during points is illegal and the referee should step in and tell her to shut up, tennis great John Newcombe says.

The Australian former world number one, who won seven Grand Slams, has urged opponents to demand she keep quiet.

"I think it's illegal," he said of her squealing.

"If I was playing against someone who was doing it all the time, I would ask for the referee and say the player has to stop.

"They're deliberately obstructing me from hearing the ball coming off the strings," he was quoted as saying by the Herald Sun.

"It's actually what I consider legalised cheating, because one of your great senses that you have on a tennis court is your ability to hear the ball come off your opponent's strings."

Last year Wimbledon referee Alan Mills, the tournament's chief official for 22 years, called for a crackdown on grunting and squealing, saying the rules needed to be changed.

"Many of the non-grunting players are unhappy about the noise pollution, and a kind of counter-grunt culture has emerged in recent years whereby offended parties ape their opponent's noises," he said, according Britain's Sunday Times.

He added: "Officials can only act if the player is shown to be making the noise on purpose, which is virtually impossible to do".

The Sunday Times said at the time that Sharapova's grunts had been measured at 100 decibels, roughly the same volume as small aircraft landing nearby.

Sharapova produced a full repetoire of squeals and grunts in her quarterfinal victory over compatriot Nadia Petrova at the Australian Open on Tuesday. But Petrova said it didn't really bother her.

"If it did, I would definitely go tell him (the umpire)," she said after being beaten 7-6 (8/6), 6-4.

"I don't see any problem. Monica (Seles) did the same. I think no matter how hard you grunt, I think you can still hear the ball coming from the racquet, especially in the arena. The sound is much higher."

Tennis has had its fair share of squealers and grunters over the years, not least Monica Seles, whose loud grunts were a trademark of her game. She has previously leapt to Sharapova's defence.

Serena Williams is also a known grunter, while Tommy Haas proved in his match with world number one Roger Federer at the Australian Open on Monday that he is up there with the best grunters in the game.

Jimmy Connors is widely credited as being one of the first major grunters in tennis.