I noticed that Sebulba's voice is very low in pitch before the race, and it is much higher during the race. Why is it so?
Before the race Sebulba is very relaxed: he's getting a manicure (pedicure?) from some beautiful alien ladies, and is trying to impress them with a deeper, more powerful voice.
During the race Sebulba is tense and stressed. Anxiety and stress can have an impact on the pitch of a person's voice. And pod racing, even if you're experienced, will most certainly raise your stress levels