There is a variant of the Optimus Prime voice changer helmet out there with Peter Cullen doing the Optimus Prime voice. I have shot a quick video showing how to identify the variant, and I also demonstrate the sounds if anyone is interested. http://www.youtube.com/watch?v=hOQqBEpphGM
I wondered why the helmet they had at Walmart this morning sounded more like Cullen than the other >_>