It's perhaps not the perfect metaphor. But up till now all we have really directly observed from outside[1] our solar system are electromagnetic waves(of various wavelengths including visible light), and this is something quite different.

http://gmunu.mit.edu/sounds/sounds.html has a bit more info on why scientists tend to use the sound analogy when talking about gravitational waves.

[1] Maybe not entirely true, we have convincing evidence of some extra-solar dust reaching earth too..