SAN FRANCISCO -- Ever since Sean Lennon stepped into the musical spotlight with his debut album, Into The Sun, he has developed a reputation for his sweet-pop sensibility.

So when the 22-year-old singer and his band stepped onto the makeshift stage set in the corner of the cavernous Amoeba Music here Thursday and suddenly filled the record store with a loud growling noise, many members of the crowd covered their ears, stunned at what they were hearing.

Not only was this the biggest free in-store performance ever hosted by Amoeba Music, it was setting itself up to be among the noisiest.

It seems that a malfunctioning guitar may have been the culprit. Soon after a roadie handed Lennon a new six-string, the growl disappeared and Lennon led the band into the soft and subtle intro to "One Night." And without anything in its path, the young singer's tender voice traveled out over the several hundred attendees stretching from the record store's folk LP section clear back to the bin of North African tribal music cassettes.

This was the Sean Lennon people had flocked to the store to see.

The performance was a rare chance to catch the son of late Beatles leader John Lennon perform in the small, intimate setting of a record store -- and for free, no less.

The young Lennon stood relatively still on the cramped stage, wearing a bright-orange mechanic's jumpsuit and strumming a Les Paul guitar. While he played guitar and sang, he was backed by a second guitar player, a keyboardist, a drummer, a bassist and Cibo Matto bandmember Yuka Honda, Lennon's significant other, on the turntables.

The huge turnout for the free in-store appearance seemed even larger than the crowd that came to see art-rockers Sonic Youth perform in the same record store only two months earlier. Perhaps because, unlike Sonic Youth, who were in the midst of a three-night stint at the Fillmore at the time, Lennon and company were only in town for a single, sold-out night at the much smaller, 600-capacity Slim's.

The assembled crowd was as diverse as the material on Lennon's album. There were middle-aged Beatles lovers, bleached-blond and leather-clad trendsetters and a gaggle of young high-school girls who came early to make sure that they got to stand right in front of the small, raised stage.

Melanie Davis, 15, came to the show with her father. "I was mad that I couldn't get into the show tonight, so I dragged my dad down here with me to see this," she said. When asked about his impression of the show, her father, Richard Davis, said simply, "Too loud."

Lennon and company seemed determined to explore the loud as well as the quiet sides of rock 'n' roll. The soft intro to Lennon's "Mystery Juice" sounded like it could have been a studio outtake left on the floor by the Fab Four after the production of their final studio album, Abbey Road. When the band mellowed and Lennon was allowed to softly emote in his unassuming voice, the music was elegant yet earthy. When the band turned it up and charged through the Black Sabbath-inspired power chords of "Spaceship" (RealAudio excerpt), Lennon's voice was barely audible.

Still, it lilted over the fiery distortion, sounding much like the grunge-pop outfit Weezer.

Lennon's noodly guitar solo in the middle of the LP's first single, "Into The Sun" (RealAudio excerpt), sounded a bit like '70s stadium-jammer Steve Miller on an off night, but that didn't stop the crowd from dancing in place. After only three songs, Lennon announced that the band was only allowed to do one more, leaving the crowd unsatiated.

Before playing the final song, Lennon told people to buy his new CD, boasting that it was, "The must-have CD of the summer."

And, apparently, the sales pitch worked.

Soon after the short set, a call went out over the intercom; employees were scrambling to find more copies of Into The Sun to put out on the shelf as visitors took the opportunity to purchase a copy. For his part, Lennon stuck around to sign copies of the CDs that people had purchased.

The swift sales of the album didn't surprise 25-year-old record-shopper Marcus Kaye. "I predict a run on Sean Lennon CDs. After that performance, everybody's going to want a copy."

All told, more than 125 Lennon CDs, albums and tapes were sold that day, according to an Amoeba salesperson.

"It was the biggest in-store performance we have ever had," said an Amoeba employee who went only by the name Joe.