Audiobooks usually do not include sound effects.
However, you may have heard effects in some audiobooks and know their usage is growing in popularity. You may want to add them to your book.
Your rights holder may insist you include effects.
Don’t do it.
Audiobooks are not a radio or TV show, movie, podcast, stage production, or game where effects would be utilized and expected by the audience.
Instead, an audiobook is an intimate performance of the storyteller right in the listener’s ear, usually by a solo narrator, though dual, duet, and multi-cast reads are increasingly in demand
Our job as a narrator is to connect the listener to the author’s words and message through our performance. A sudden sound effect could be jarring to the listener and take them out of the story.
Beyond that point, effects can not be added arbitrarily to the narration. Any effects need to be planned in advance and executed with precision by someone who is experienced in mixing audio.
Most narrators do not have either that depth of engineering skill or the time and need to acquire it.
Acting choices and mic technique should be used instead of sound effects.
The producer, not the rights holder, has the final say on the decision about production choices. As the producer, you should just say no to effects.
Some audiobooks are audio dramas with rich, layered music and effects throughout the book like a movie soundtrack. You can hear the difference between an audiobook and audio drama by listening to the retail samples of the 2 versions of 1st to Die by James Patterson:
Booktrack version (music only)
Even though the books are in a popular series of 25 titles by a very popular author, the publisher only made the first 2 books available with music and effects. The Booktrack versions were published in 2018, which seems to indicate the publisher is not producing more of them in this series.
Many audio dramas include a full cast. Listen to the difference between the 2 samples of Ordinary Magic by Devon Monk:
GraphicAudio version (full cast, music, and effects)
The production costs go up significantly in hiring an engineer to plan and implement sound design in a book. As you can see in the examples, the Booktrack and GraphicAudio editions have a higher price.