There is an odd, comfortable lack of ritual at small club gigs. Maybe it’s low cover or perhaps it’s the close, congenial atmosphere, but people don’t seem afraid to miss a song or two most nights. People drift in from the bar as the music rustles up, casually finding the right spot, occasionally leaning in to talk to a friend. An exception came two weeks ago, on a Saturday night at Kings in downtown Raleigh. A tall stranger in a white cowboy hat and a sort of vivid, anti-camouflage orange shirt abandoned his perch among a group of five friends five rows back. He headed to the bar as another pal slapped a five in his hand, asking for two more bottles of brew for the coming set.

As he was steps away from leaving the crowd, though, the packed, smoky, sweaty and sold-out house erupted. There they were, The Avett Brothers: two bearded boys and a burly, polished upright bass player, taking the stage for a crowd that wanted it. The beer-fetch wanted it, too, immediately turning, retracing his steps and joining the fanfare. The beer could wait.

For those three fellows, defining it is difficult at best. These Avett Brothersthat is, Scott and Seth Avett with bassist Bob Crawfordplay sometimes sweet, sometimes sour rock songs with three voices, a banjo, a guitar, a bass and a foot drum. It’s a Gordon Gano pipedream of Richard Manuel and Rick Danko jamming by the riverside with Jagger and Ronnie Van Zant.

That’s not enough, though: These are stories navigated with a sense of adventure and honesty stripped from folklore and folk music, respectively, but they’re played with reckless abandon, a spirited rock enthusiasm that implies “Oh, fuck it” much more than it does “Aww, shucks.”

That’s the it. With two girls on his arm and several beers under his belt, the man in the orange shirt lights into the first couple of songs, singing at the top of his lungs with the ebullient “At the Beach,” bouncing along to the punkish country songs like a cowboy reared on the Pogo, not the Two Step. This is fun, and this is smart, maybe brilliant stuff. People dance and sing because of the former, but they know the names of the members in this local-for-now band because of the latter.

Maybe that’s not it, either. Perhaps it’s eclecticism in this three-piece that is it for this crowd. After all, back in Concord as kids, Scott, 28, and Seth, 24, cut their musical teeth memorizing the melodies of Hall & Oates, Michael Jackson and Duran Duran. Seth committed himself to mastering the piano, while Scott became the eighth grader with Van Halen, Hendrix and Zeppelin insignia scrawled across his notebooks.

“I remember looking across the room and seeing kids being into some of those things and music, but they wouldn’t be as far into Zeppelin as I was,” Scott says, on his way between his Concord hometown and his current home in Mars Hill. “They were into football or class or something.”

Scott joined his first band that year, and he remained in at least one outfit throughout high school; meanwhile, Seth was working behind the piano and the guitar, constantly practicing and eventually gaining his older brother’s respect as a substantial talent.

“We both started taking lessons early on, and he passed me on that because he has more of an attention span. He was able to think things out more organized than I would,” Scott says, adding that the four-year age difference beset any sibling rivalry but encouraged cooperation.

At East Carolina, Scott played in a handful of punk bands while forming a Tuesday night bluegrass jam circle on campus. Meanwhile, Seth went to Merlefest for the first time, spending most of a day at the Wilkesboro festival with bluegrass patriarch Doc Watson, learning and listening.

The pair began working up a batch of old-time folk, often exchanging scraps of verses and choruses over long-distanceSeth back in Concord and Scott in Greenville.

“One of the first songs we did like that, there was a part where he moved along with a melody and so on, and we thought we had it,” Scott remembers. “When I got together with Seth, though, he had developed it in another way than I had. Things like that would happen a lot.”

Those long-distance miscommunications slowed after Seth joined his brother at East Carolina following high school. Their band Nemo rose from the ashes of Seth’s Margot and one of Scott’s punk units. The brothers would often open incumbent punk house concerts with acoustic guitars, daring art students and hardcore fans to appreciate the woods they came from.

When Nemo fell apart, The Avett Brothers took shape, throwing that punk energy into reinterpreted traditional and iconoclastic bluegrass rockers. The rest is the band’s rising action, an endless stream of gigs, songwriting and recording that threatens the boundaries of what it means to be country or how a banjo should be played at a bluegrass festival.

Mignonettea concept album based on a true story of survivors, cannibals and one honest man that emerged from the 1884 wreckage of a British yacht by the same nameis the band’s most consistently ebullient and charged record yet, a perfectly unorthodox concoction of underage rock tendencies, mature songcraft capabilities and defiant genre-busting concepts. This stands as the band’s best chance yet to break into some sort of national spotlight, andwith national distribution by Sony, a few prominent magazine features and a busy touring itineraryit may happen.

At this moment, The Avett Brothers seem able to capitalize on this strange brew across the board: Their off-kilter, free-for-all style would probably catch the ear of jamgrass fans, while their on-stage zest and abandon makes them a natural fit for the rock club. But these songsfrom the Jack Johnson, pure pop bubbles of “At the Beach” to the giddy feelings of country beamer “Swept Away”are gems that demand not to be confined to any underground.

“We don’t know if we’ll ever make it on to any charts. We believe that it could and couldn’t happen,” says Scott, pulling into his Mars Hill driveway. “To us, this is extremely serious business, and we were brought up with a really strong work ethic. My dad laid that out for us, so we’re willing to make sacrifices for this thing.”

As for what “this thing” is, well, exciting is perhaps the only sufficient answer.