Only note I'd like to throw in is that I would've loved to hear more of the mechanical noises, like in the Bay movies..? They're machines, they make mechanical sounds. Go to a machine shop or a mechanic shop and record real-life sounds, e.i. air pistons, impact guns, lathes or drill presses, etc. Or hell, hit up GM testing factories for their impact testing videos, and use the sounds from there! Don't just use artificial sounds, or that's what it'll feel like - artificial... ^-^
Oh you hear that more for Bumblebee and Ratchet. Bee has extra sounds sounding like jangling keys while Ratchet's sound is accompanied by... well a ratchet.