TFW2005 has posted their interview with Transformers voice actor Mark Ryan. He is the voice of Bumblebee and Jetfire for the movies and usually does voices of the Transformers on set with the actors to help with timing of the "human" lines as usually the formal voice over recording for the Transformers is done later. In the interview he talks about how got hired, working on the films and voicing the characters. Below is a section that specifically is about Transformers 3, the rest of the interview is here.
TFW: Can you tell us anything about what's happening with TF3? What do you see yourself doing in Transformers 3? Will you be continuing as the on-set voice? What would you like to be doing?
Ryan: I am back onset and doing the voices again. There are several new robots, which I’ve played during filming but I can’t give details for obvious reasons. I do feel the storyline for TF3 is the most intriguing one in the series, so far. It’s an area I’m personally very interested in and find the history fascinating. Anyone who’s read The Pilgrim will know about these associated subjects. Having spent a part of my life in the military and in the more esoteric areas of intelligence work myself, I find the back-story for this one to be really cool. Also, the cast is just amazing! I’ve already worked with Frances McDormand and I was blown away with her good humor and down-to-earth approach to the size and scope of the project. Obviously working with both Shia and Josh is always a real honor and joy and I must give a shout-out to Harry Humphries and his SEAL team boys, who really bring the heat.