Interesting. I thought that too. But it's a muffled "Thank You."
I think the Cube had something to do with repairing his voice. The book, however, does not explain it, like I had hoped it would.
Hmm......
Um, mentioned the "Thank you" in the original first post. He definitely doesn't "say" it, just makes the sound that is obviously mimicking it. Still - Frenzy was repaired almost instantaneously when coming in contact with the Cube. If it was the Cube that fixed BB's voice, it should have also been instant. Nothing seems consistent about the explanation. It only doesn't make sense that it was fixed at that point in time because BB still chooses not to speak. One of the best moments for him to have done so was after his legs got blown off and he gives the cube to Sam. At that point he should have spoken for the first time and said, at the very least, "Goddam, this hurts like a mofo!! Here, take this mother-effin' Cube and run 'fo Megatron kicks your arse!".
When does it happen, during what scene?
As far as the black aura people keep talking about. The only time I remember seeing it is when Lennox is sliding underneath Blackout and is shooting up under his armor. The reason I remember this is because the 2nd disc has excerpts from the filming of this scene and he (Josh Duhamel) talks about how he's sliding away from the bike in the scene and Bay wants to do it again because he wants the camera to focus differently.
When I watched the movie again after you can see that when the camera is on Lennox from the top down the aura is there - perhaps to block out some of the things you are not supposed to see caught on the edge of the film. Other than that, I don't recall more scenes with the blackness.