Rumble and Frenzy were sent on a spying mission and never returned, it was long ago assumed they were discovered by the enemy and killed.
Soundwave still hopes they will somehow come back, despite the fact that the Deceptidragons have been constantly on the move and are nearly impossible to find.
This is not set on Earth, however it is an organic planet that is very similar to earth, but it is bigger and has several moons.
On Tumblr: [link]
Transformers Prime/Soundwave © Hasbro
Art © Me