It turns out Prowl's hologram of a human police officer is actually what he would look like as a human.
Optimus Prime's human form looks almost exactly like a cartoon version of his voice actor, David Kaye.
Soundwave references the original Soundwave's famous line from The Transformers: The Movie (1986), "Soundwave superior. Constructicons inferior." as he puts a spin on the quote and says "Autobots inferior. Soundwave superior.".