Based on the pictures below, it appears that pre-production in Transformers 3 is in full swing with a TF3 set being built at the Playa Vista soundstages. The location has been used before by director Michael Bay for the previous Transformers films.
Here is what SuperHeroHype's source reports:
Well, Transformers 3 is gearing up there. I've attached pics of the sign I stumbled upon at the warddrobe department just to offer a little proof. When I peeked inside, posters for both Transformers were hanging up and clothing racks had tons of military gear hanging from them. Above one rack it read "Iranian Army." Above another rack it read "Ukranian Army" and above a third rack it referred to "Matt" ("Matt's costumes").To summarize, something may happen on the moon, there could be a character named Matt, and once again the story makes a visit to the Middle East (as indicated by an extras casting call). Thanks to David for the link.
There's some big stuff being built here, man. One end of the soundstage had some wooden structures. Another area they were chopping away at styrofoam to create a rocky terrain. And the crew was rolling along something that looked like a giant gear. I breezed on by the "model" shop and, while I couldn't get a good look inside, there were a lot of moon reference photos and NASA moon lander pics. I could have sworn I saw a Transformer, again, didn't get a good look.