Trying to find 'My Vampire System' as a full, free audiobook is a bit like hunting for a specific shade of moonlight—possible, but you need to know where to look. Legally, the options are pretty limited. The audiobook is produced on platforms like Audible and Google Play Audiobooks, which use a purchase or credit system.
You might get lucky with a free trial. Audible often gives you that first credit to use on any title, and if you're new, that's essentially a free grab. Some public libraries have partnerships with apps like Libby or Hoopla, so check your local digital collection. They sometimes have popular web novel adaptations.
Beyond that, full free listens on random websites are almost always unofficial and sketchy. The quality varies wildly, and it's often a text-to-speech robot voice that murders the pacing. I tried one for a chapter and the monotone delivery completely ruined the tension of a fight scene.
Honestly, if you're invested in the story, the official route supports the author, Jinho Ko, which matters for ongoing series. Maybe start with a free sample chapter on Audible to see if you like the narrator before committing a credit.