At some point after the Battle of Mission City, Sideways came to Earth to find his great leader Megatron had died. He went into hiding from the Humans, finds refuge behind the giant Construction Demolishor.
Revenge of the Fallen
When a team of N.E.S.T. And Autobots got an Energon reading on Demolishor, he transformed and attacked, prompting Sideways out of hiding. Realizing their were in fact two cons present, N.E.S.T. Sent in Sideswipe, who chased Sudeways until he threw two blades at the con and used them to cut Sideways in half, before he could transform again.
Sideways is not DOTM Soundwave