It could have been the chanting and clapping and shouting as thousands draped in green and white walked towards their gates, or the hooves against the ground, horses patrolling, with police perched on top.
There were flares smacking on pavements and helicopters in the sky, feet climbing steps and hands slapping on backs.
"Just listen to that," said Real Betis fan Jose Maria, pointing behind him. "That's the sound of a football match."
It was 728 days since the last Seville derby had been played with fans, another welcome reprieve for supporters in Spain but this one perhaps the most welcome of all.
If the Clasico between Real Madrid and Barcelona is La Liga’s most famous fixture, 'El Gran Derbi' between Sevilla and Real Betis is the one most synonymous with supporters, a celebration of devotion and loyalty to two teams situated just four kilometres apart.
"I took a boat and a bus to get here," says Juan Carlo, who has been a Betis socio for nearly 50 years.
"Without fans this game was terrible, to be honest it was nothing. With fans, it's the best game in the world."
It was also the first match without any fans at all, the starkest demonstration of what had changed and what had been lost.
On June 10 last year, Sevilla faced Real Betis as football resumed in spite of the pandemic, in front of empty seats, with players arriving in kit and people locked down at home.
- 'Absence of magic' -
"To return is to win," ran La Liga's slogan but even if the victory was necessary and better than nothing, it felt hollow.
Amid nervousness about coming back, Sevilla midfielder Ivan Rakitic was among the loudest voices in favour.
"I have heard a lot of talk about us having to play for economic reasons but I haven't heard anyone talk about the fans, the people, for whom their club is a part of their life and it's been taken away from them. We have to step forward," he said.
There were two more derbies, including the 100th in the top flight, and all of them felt diminished, like games everywhere, but perhaps in this game more than anywhere else.
"In the absence of magic, all that was left was metal studs," wrote El Mundo.
Joaquin, Real Betis' iconic forward, who joined the club aged 16 and turned 40 in July, even renewed his contract for another season, determined not to retire without people in the stands. "It would make me sad if my last year was like this," he said.
With Betis 2-0 down, Joaquin came on as a substitute in the 89th minute on Sunday, applauded by those home supporters that were left.
Just over an hour earlier, hundreds of green and white flags fluttered around the pitch as 50,534 fans, minus Sevilla's 600, sang the Betis anthem.
"Hay una leyenda que recorre el mundo entero," goes one line, "a legend that runs throughout the whole world."
In the afternoon, clouds of red smoke had covered the Sevilla team bus as thousands waited to greet the players arriving at the doorway of the Lebreros hotel.
On Saturday, they had waited to serenade them after a last training session at the Ramon Sanchez Pizjuan.
"Tomorrow the essence of the derby returns, the fans," said Monchi, Sevilla's sporting director.
"Betis and Sevilla fans were born with this feeling. Let's show the world what our derby is: 90 minutes of passion and dedication for the colours, for our coexistence, and respect for the rest of the season."
Sevilla, in third, were took strong for Betis, in fifth. Shortly after half-time, Marcos Acuna rifled a shot into the top corner and with nine minutes left, Hector Bellerin diverted into his own net, prompting Betis fans to turn for home.
At almost 11pm local time, with most of the stadium empty and the final whistle long gone, Sevilla's players skipped back out onto the pitch.
In the far right corner they danced, the last sound of the match Sevilla's fans high up above them and still there, celebrating the night the derby returned.