The lyrics "I'm not making the same mistake / Won't be putting my heart on display" refer to past relationship trauma that has made him hesitant to be vulnerable.
Puth described the "too-loud" guitars as representing an overactive brain that can't sleep due to racing thoughts. Musical Composition Charlie Puth - Charlie Be Quiet! (Lyrics)
Charlie Be Quiet! - song and lyrics by Charlie Puth - Spotify The lyrics "I'm not making the same mistake