I think it's 50/50 on whether Soundwave was Megatron's . You could say that Soundwave's loyalty and willingness to do whatever Megatron commanded would be evidence that he was Megatron's . However, when Starscream threw Megatron out of Astrotrain, Soundwave did not stop Starscream from doing it. I think that might be the reason Soundwave was basically demoted after Megatron became Galvatron. Cyclonus was Galvatron's main guy.