Velvet Generation: Ashcan (2002)

From the introduction:

No one knows exactly how those fateful radio waves made it so quickly across the Milky Way to the now-nameless planet the aliens called home, just as no one knows why they abruptly stopped, inspiring the century-long pilgrimage across cold space to the birthplace of rock music. A handful of hardcore geeks within the revolution still maintain that it should have been impossible, but the effect was undeniable, having changed both planets and their inhabitants forever. At that time, the aliens didn’t call themselves Starchildren. They looked nothing like us; the most they can recall of their natural state implies they looked something like an octopus or cuttlefish, though back then they were even more capable of changing their forms, so really, who can say?