I've seen people report that he plays different sound effects in both modes if you plug a MechTech weapon into the active MechTech port (the one with the button inside it). I think it's the one on the left side of the truck.



They would have done the electronics for Sentinel Prime long before Bay cast Nimoy, I think. But yeah, most of the talking Movie Optimus Prime toys since the running change of the Optimus Prime helmet in 2007 have used Peter Cullen.