Answer
It becomes thermal energy.
Work Step by Step
Sound waves jostle air molecules as they pass by, and ultimately, the sound energy is transformed into thermal energy, warming the air ever so slightly.
This is discussed on page 379.
You can help us out by revising, improving and updating this answer.
Update this answerAfter you claim an answer you’ll have 24 hours to send in a draft. An editor will review the submission and either publish your submission or provide feedback.