Random crack thought, but, and bear with me here, TFA Megatron (before Earth, ideally) somehow end up interacting with the Decepticons of another continuity, and he sees that they're doing better than his Decepticons (as in, hadn't lost yet) despite the Autobots of this world being bigger and more adapt at combat with some war frames of their own. And he's trying to figure out the differences (at least ones that he can control) and see what he can do to improve his odds.
He noticed that the chain in command is practically the same, that is with one exception. A third in command (I honestly don't know who's TFA Megatron's third or if he even has one, at least at the moment, so let's say he didn't have a third since their loss, OK?) Soundwave.
Now, he never known a Soundwave, both in Decepticons and Autobots ranks. So he's curious about this new mech who not only a chief officer, but also seem to be trusted implicitly by the other Megatron with both his back and the tasks he assigned to him (TFA Megatron has loyal subjects, Like Lugnut and Shockwave who would do anything in their power to serve him, but they tend to go overboard with their attempt to appease him and to show up each other. Soundwave doesn't seem to have such issues. If anything, he's quiet).
Another thing that caught his attention that the other Megatron is familiar with him, and doesn't have that detachment that TFA Megatron keep even with his more loyal solders. He favors him but not in a 'keep this up and I will keep reminding everyone of how well you're doing', but it a genuine acknowledgment of his competent and a job well done that is accepted quietly and without commotion or gloating.
Anyway that is all to say; TFA Megatron sees a Soundwave and decides "I need one of those." XD
