NEW YORK >> When heavy rain began pelting the closed roof at Arthur Ashe Stadium, Andy Murray couldn't pick up the usual sounds of a tennis match.
Most importantly, he said, the thwack of a ball coming off his opponent's racket strings — or his own, for that matter — was completely indiscernible during a 6-4, 6-1, 6-4 second-round victory over Marcel Granollers at the U.S. Open on Thursday.
As it is, the $150 million retractable cover making its tournament debut this week makes the main stadium louder because the structure, even when open, traps the sounds of spectators chatting in the stands.
When it's shut, as was the case Wednesday because of showers that delayed play on all other courts for hours at a time, the roof amplifies all of that ambient noise.
And when the drops came down early in Murray's second set, well, it was loud as can be.
"You can't hear anything, really," 2012 U.S. Open champion Murray said. "I mean, you could hear the line calls."
But that was about it.
As Murray and Granollers played, there was a constant din during points, an amalgam of the downpour bouncing off the outside of the roof and the murmur of the crowd bouncing off the inside. From a seat in the 10th row parallel to a baseline, the racket-ball impact was rendered silent by a louder version of what you hear when you hold a seashell to your ear.
It's not simply that it's an unfamiliar soundtrack for a Grand Slam match. It affects the competition.
"We use our ears when we play. It's not just the eyes. (The sound) helps us pick up the speed of the ball, the spin that's on the ball, how hard someone's hitting it. If we played with our ears covered or with headphones on, it would be a big advantage if your opponent wasn't wearing them," Murray explained. "It's tricky. You can still do it, but it's harder, for sure."
Granollers offered a similar take.
"We're not used to playing with that noise. ... I was not feeling like I was hitting the ball right. It was difficult also to concentrate. Tough to play," Granollers said. "There is more noise with the roof, but, I mean, if it's not raining, it's OK. With the rain, it was too much."
Like Murray, he acknowledged players will need to learn to adjust.
"When it rains, you're going to get noise," U.S. Tennis Association Executive Director Gordon Smith said, when asked about the players' comments about the ruckus.
"We will look at potential ways to attenuate some of the noise going forward. It's going to be louder than it was. We knew that. And it's something the players will deal with and the fans will deal with."
The good news: At least Murray, Granollers and others were able to play. Rain has often been a schedule-wreaker at the U.S. Open, where the men's final was postponed five consecutive years from 2008-12.
Because of Thursday's wet weather, action around the grounds was limited until the early evening — but matches kept coming under the roof in Ashe, including Serena Williams' 6-3, 6-3 victory over American wild-card entry Vania King at night. That pulled Williams even with Martina Navratilova's Open-era record of 306 Grand Slam match wins; only Roger Federer, with 307, owns more.
"It was definitely a little different playing with Ashe closed," said Williams, who produced 13 aces yet clearly was displeased with winning only 13 of 40 points on King's first serves. "But it still feels great."
Chair umpire Alison Hughes repeatedly asked spectators to keep it down.
"Your voices are carrying to the court," she said. And: "Ladies and gentlemen, respect the players. Please remain quiet."
Men advancing included No. 6 Kei Nishikori and No. 8 Dominic Thiem, but No. 16 Feliciano Lopez lost to Joao Sousa 6-2, 6-4, 1-6, 7-5.
Juan Martin del Potro, the 2009 champion, was scheduled to face 19th-seeded Steve Johnson of the U.S. later Thursday.
Earlier, Williams' older sister, seven-time major champion Venus, beat Julia Goerges 6-2, 6-3, while No. 5 Simona Halep eliminated Lucie Safarova 6-3, 6-4 in a meeting between past French Open finalists that was the first contest played entirely with the roof closed (it was shut for the first time during a match midway through Rafael Nadal's victory Wednesday).
Serena is seeded No. 1, and Venus is No. 6.
"It's really amazing to have, you know, myself and my sister in the top six. It's pretty cool. It's a great feeling," Serena said. "We're still just doing the best that we can."