Small mod that replaces the "3, 2, 1, Go!" with Gran Turismo's iconic countdown noise.
Optionally replaces the "Start your engines" dialog with some Gran Turismo race start jingles.
Although it was made for Platinum, it should work with Vanilla as well.
Original & GT2 Only Preview:
Polyphony Digital - Countdown noise and start jingle (Gran Turismo, Gran Turismo 2, Gran Turismo 3, Gran Turismo 4)