Question: Cinema Sins pointed out in the progress bar of the computer display that the word Percent is spelled with a hyphen. Like Per-Cent. I am aware that the word can be correctly spelled as percent and per cent. But doing some research the only mention I can find of it spelled with a hyphen as per-cent is just mentioned as an old way of spelling it. How old is that? And is it still within the time frame of this late 80's period movie to be spelling it as Per-cent on a computer display? https://youtu.be/HNri0mNI2PY?t=1159.
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.