In March of 2020, it had been four years since I had done any soldering, so for the sake of nostalgia and practice, I put together this simple Elenco Sound Reversing Car Kit that I had gotten from Pololu years earlier.
It drives forward until the microphone picks up a short sound (including bumping into something), then it reverses for a few seconds. A spring causes it to pivot left while it reverses, so it then drives forward in a new direction.