According to a recent episode of Unscripted, James Avery has been cast to voice Silverbolt in Transformers 3. If James Avery is familiar it might be due to the recent commercial were he is the professor that supposedly has a video lecture go viral. He also played Philip Banks in The Fresh Prince of Bel Air.
In the video he discusses his career and life. Oddly though is the blurb on the site describing the actor which says "He is also currently working as voice talent for the upcoming "Transformers 3" film (set to release in 2011), playing 'Silverbolt'." This information is not repeated in the video interview so unknown if this is from Avery or some other source.
Silverbolt has been around since the Generation One days with an alt mode of a Concord SST jet liner and leader of the Aerialbots that formed Superion. The name was used again for Beast Wars as a noble knight character that was a fusion of an eagle and wolf. Long story short, the character has history that is a perfect addition to the movie cast of characters.
As for feasibility of the rumor, who knows really but for now I now take it with reservations until more information comes out. With Transformers 3 pre-production underway and at least a draft or two of the script likely completed, it is possible that casting has already begun. However, for the two previous films it seemed that Bay always waited until after the film was nearly complete before he started nailing down the voice roles and their lines. Maybe this time he decided to change up the process. Either way, as a fan of the actor I hope this works out. Thanks to Chris and RY for the link.