Final answer:
The Beach Boys' album Pet Sounds is notable for its complexity, influence on popular music, and innovative sound exemplified by the inclusion of a train whistle in the song "Caroline, No."
Step-by-step explanation:
The Beach Boys' album Pet Sounds is significant for several reasons. It represented a major transformation in the band's music, showcasing complex productions and sophisticated songwriting that departed from their earlier surf rock style. The album was highly influential, affecting the course of popular music with its innovative use of harmonies, arrangements, and recording techniques. Pet Sounds is often considered one of the greatest albums in music history, with its influence felt in many subsequent musical movements and recordings.
One interesting auditory feature of the album is the sound of a train whistle at the end of the song "Caroline, No." This sound starts at approximately 2:20 in the track and is a fine example of the innovative and experimental aspects that Brian Wilson, the key creative force behind the album, brought into the Beach Boys' music.