Plot hole: How can Bumblebee and Optimus already have the car specs and colours before they leave Cybertron for the first time to come to earth? Optimus didn't have this when they came to earth in the first Transformers movie.
Suggested correction: First of all, this might not be the same continuity as the older Transformers films. Second of all, the cars on Cybertron might be Cybertronian vehicles. Optimus scanned the semi in the first film so that he could be a different vehicle than he already was. There is no reason this could not have happened.
I'd like to add that we know for a fact that this is not the same continuity. It is a reboot. See the Wikipedia article.
Question: Why didn't Frank Welker reprise his role as the voice of Soundwave for this film?
Answer: I couldn't find any other information, but honestly... Soundwave is barely in the movie. Probably just wasn't worth it for the production to pay Welker to come in just to record a few throwaway lines.
I considered that possibility as well, but since Peter Cullen reprised his role as the voice of Optimus Prime yet again for this film despite Prime's minimal involvement, it doesn't quite wash. Also, given Frank Welker's highly prolific voice acting career, it's unlikely he would have declined on the basis of pay or importance of his involvement.
Soundwave was barely in the movie (he's literally only in a few shots) and only had one or two lines. As the other answer suggested, it probably just wasn't worth it for the studio to pay Welker to come in, or they just didn't feel it was necessary given that Soundwave was essentially just a blink-and-you'll-miss-it cameo. Optimus has a much larger presence, and Peter Cullen's voice is pretty synonymous with the character in the film series. Hence, it was worth it to have him return.
