If Bumblebee gets his voice back, he should sound like a kid IMO. He acts like a kid throughout the movies, so I imagine that he is the Autobot equivelent of a kid or a teenager. He has a wide-eyed innocence about his character design, and his mannerisms are very playful and "cute." His voice from Transformers 1 sounded totally mis-matched to me, because I was expecting him to have a more cute and youthful sounding voice. Instead, he sounded like that Persian guy who falls down the well in 300, and that didn't work at all which is probably why they went back to the radio.
If they did change his voice, they could easily just explain that when his voice came back in TF1, his processor was still significantly damaged, which would also explain why it reverted in Transformers 2. When he actually does get his voice back for real, it should match his character design.