One example is if you're using Hyperthrust, the music could speed up or something, or if you make a barrel roll then the music will take on a mechanical feel, similar to what you hear in the earlier levels of Portal 2 when you start using Aerial Faith Plates.
Also, why does the Turbo pickup consume Shield Energy? I thought it would have its own fuel. You have to take into account that you have infinite Shield Energy in Time Trial and Speed Laps.