Search around for a public domain sound and inport it into MODX as a wav file. Maybe something here: https://www.audiomicro.com/free-sound-effects/free-transport-and-vehicles/free-car

There are lots of public domain sources for similar sounds.

This walks you through the process: https://www.youtube.com/watch?v=I9yR7cTg-oM

Here's another thread that covers the same topic: https://yamahasynth.com/ask-a-question/save-and-trigger-a-wav-file-within-a-performance

I have a windows PC and use Wavosaur to slice/dice audio files to prepare for import into my keyboard. This car rev is going to be "one shot" - meaning it's not going to loop. So the more advanced features I use in Wavosaur are not called for here. But if, in the future, you want to also experiment with loop points - software like Wavosaur handles this as well as the more basic operations (trim, etc).

Thanks Jason. This forum is the best1