During the Transformers 2 filming in Princeton, NJ, Sam Witwicky gets attacked by what appears to be Frenzy, who appeared in the first Transformers. The silver Decepticon seems to have crashed through Sam's windshield. Watch the on set footage from Philly Film Girl and hear Sam scream, "oh my god, oh my god, get back, get back," then click through to see pics.
The picture on the right is the on set location from TFW2005, the left is Frenzy. You could make the argument that this is a new Decepticon, as their faces look a bit different. There are rumors circulating that this may be one of Soundwave's hench-bots.
For more on set video check out Philly Film Girl.