Per the source:
"Bumblee hasn’t had a distinct voice in any of the previous Transformers movies. Producer Lorenzo di Bonaventura explained why that had to change now.
"Since we were approaching this as an origin story, we felt that it was appropriate that you got to hear his voice," di Bonaventura said. "That’s the simple logic that we employed. The longer-term implication of that is different. But the short-term implication of that is since we really are resetting the mythology, essentially, of who Bumblebee is. And so, that seemed to us to be appropriate, to get the chance to hear what he sounds like."
As for why O’Brien was chosen to be that voice, di Bonaventura said, "Dylan has that great quality in his voice of youthful exuberance, and also sort of trustworthiness. I think those are the two qualities that we wanted Bumblebee to have." "
ONTD, did you plan on watching this (admittedly cute looking) movie? If not, will you be doing so now?
(mods, I think I figured out what the problem was, hopefully it goes through this time!)
OP's note: I can't picture his voice with Bee...seems weird.