Doppler Shift

By the time she came out I had the motor running
She looked surprised like there'd be more to say
I saw her lips moving but I couldn't hear her
The helmet, the noise and my own stubborn ways
After that I tore off with pistons screaming
I guess the engine noise faded as I moved away
But if she thought she heard a hint of the motor slowing
Well that was just Doppler shift messing with her head