There was a strange sound coming from Citi Field on Saturday afternoon. One not heard much lately, and not likely to be heard much the rest of the summer.

It was cheers. Applause. Actual joy.

For 30 minutes, the Mets and their fans got to forget about the current season that is closer to irrelevance than significance, and take themselves into a time machine half of a century ago, to honor the 1969 World Series champion Miracle Mets.

As part of the festivities, the ‘69 Mets received keys to the city from Mayor Bill de Blasio and arrived at Citi Field in a parade down newly named Seaver Way. The Citi Field scoreboard was given old school graphics and fonts to look like Shea Stadium and following the ceremony, the old champion Mets met the current disappointing Mets.

“It’s great to see all your teammates, all the guys who are here having a good time,” said former first baseman Ed Kranepool, a Met his entire 18-year career. “The stories get longer. The lies get better. We were better players back in those days.”

There was sadness to the celebration. Hall of Fame pitcher Tom Seaver, battling dementia, couldn’t attend. The Mets on Thursday changed the name of 126th Street in front of Citi Field to Seaver Way and changed the address of Citi Field to 41 Seaver Way. He wore No. 41 during his career. Plans to build a Seaver statue in front of Citi Field are also underway.

“Great for him,” said Jerry Koosman, who was Robin to Seaver’s Batman in that dominant rotation and won two World Series games in 1969. “He left a lot of great memories here and that’ll remind people every time they come to the ballpark about some of those memories.”

“Without him here, there’s always a sense there’s a missing link,” outfielder Art Shamsky said. “He was the face of the franchise and obviously the face of that team that year.”

Fellow hurlers Nolan Ryan and Gary Gentry and infielder Al Weis couldn’t attend. Key players like center fielder Tommie Agee, third baseman Ed Charles, reliever Tug McGraw and manager Gil Hodges have died.

“It is 50 years later,” Kranepool said. “We’re all struggling to keep it together. I don’t think we’re going to celebrate 75.”

There will always be that magical summer, however, seven years after the team lost 120 games in its inaugural season. The Mets, who had finished in ninth place the previous season, trailed the National League-leading Cubs by 10 games on Aug. 14 before a rampaging finish to surge past Chicago, then upsetting the Orioles in the World Series in five games.

“What made this team so special and the victory so good was because of these guys lived through the loveable loser years and we were all on a pretty bad team the year before. And then to win it all makes it that much more special,” Shamsky said. “The beauty of it is everybody contributed to our success, and I think that’s one of the legacies of that team.”

Soon, reality would return. The current Mets were back on the field. The buzz was gone. But for 30 minutes, Citi Field was alive and full, awash in the fondest of memories.

“It was a year of miracles,” de Blasio said. “First man on the Moon. Woodstock changed the course of this country’s history. So many things happened. But the thing I remember so clearly is when a team from Queens not only won the heart of a city, but they won the heart of America. There’s a reason they called them the Amazin’s. It was extraordinary to watch.”