Hey customizers: get to work on this!
Think of all the Mini-Cons he could fit in his chest!
Edit: Whoops, that's not Soundwave, it's Optimus Prime! So let's borrow some text from his bio, instead:
"On Earth he would have been a Doctor, a mechanic, a scientist and a warrior, but on Gallifrey there is no difference between these professions."
It does explain where his trailer goes when he transforms, though!