Whether j-pop and j-rock and such are all just different subsets, or whether all Japanese popular music is j-pop, depends on whom you ask. Just like the American-European scene, you have all kinds of bizarre genres and orientations Noise bands certainly aren't what most American otaku picture as "j-pop," but since it grew out of the same gel as aidoru pop, it would seem to qualify anyway. Then there's image bands, some weird mutation of the managed-image aspect of aidoru pop and j-rock. It's a complex scene, and not as definable as a lot of Western fans seem to think it is.