Hello! Welcome to RRU!
Are you saying that you want the AI cars to have different voices, or you want to change the AI voice, or change the sound of the cars themselves? I'm kind of having a hard time understand your question (don't feel bad. I've had trouble getting my questions across before ), but since it relates to audio, I can help you, for the most part.
Yes, the audio is located in the gamedata, namely, LEGO.JAM. You will need to extract it in order to access the audio. Pick up JrMasterModelBuilder's JAM Extractor, and extract it. Next, after you locate the audio you want to change (it will have a .pcm file extenstion), read my tutorial on how to mod the LEGO Racers audio. Be sure to take into account the fact we don't completely understand the audio format yet, so the audio you add will not sound perfect in-game. Also, the AI voices are completely broken, so you'll need to consult that topic for the files you'll need to change. Once you mod the audio, recompress your files back into a LEGO.JAM (be sure to back up the original one!), and load the game. If everything works, you have sucessfully modded the audio!
Those are general steps on how to mod LR audio. Once I can completely understand your question, I will be able to give you more detailed info.
Greetings from the US
-le717