Amid the relentlessly changing cityscapes of Beijing and Shanghai, a new kind of music is being made. In terms of its discordance and abstraction, it compares to Dada, or the New York City and Berlin avant-garde movements of the 1970s. Yet something about it — a certain urgency and iconoclasm — could only have been spawned amid the wild experiment that is modern China itself. The country’s punk and alternative-rock scenes have been gushed over by excited commentators, eager to cite them as evidence of China’s changing mores. But they are staid in comparison to that created by a new breed of artists, who eschew conventional guitar-based music in favor of baffling electronica, extreme noise and found sound.