On Tuesday, he made a surprise appearance at the band's concert at the Best Buy Theater in New York's Times Square.
Before Goldfinger launched into a set of ska hits, Manganiello introduced the band onstage.
The band was a co-headliner in a lineup of the Don't Stop Skankin tour, which brought together ska veterans Reel Big Fish, Orlando-based Beebs and Her Money Makers (who covered Miley Cyrus's "Wrecking Ball"), and Kansas City rockers, Beautiful Bodies.
"Joe seemed very excited as he brought Goldfinger to the stage," an onlooker tells PEOPLE. "He even told the crowd how he used to roadie for the band almost 10 years ago."
The source adds, "Backstage, Joe was in great spirits and seemed very excited to watch his friends put on an amazing show."
As the night continued, Manganiello mingled with fans and recounted his days on the road.
@joemanganiello introduced Goldfinger at their NYC show with Reel Big Fish! Fun.— Greg Singer (@gregoryrsinger) November 13, 2013