The North Bronx, long a metro flyover zone of ethnic enclaves, old man bars, Medicare recipients and nursing homes, is a place known for neither enticing day trippers nor inciting giddiness. Yet on consecutive weekends now an unlikely mix of Manhattan hipsters, Westchester teenagers, college students, rock journalists and music industry cruiserweights has there found themselves united and turned on by an improbable phenomenon. Packing off-the-grid, wood-paneled, un-ironic lounges and catching bands with names like Sweetfart (average band member age: 75), Nothing2 (averageage: 71) and Grand Mal Seizure (average age 83), they afterward engaged in long searching stares. As if to say, “You thinking what I am? This what it looks like? I’ll say it if you will: could it be at last a major new American rock scene is ready to pop?”