Is there a frame story structure in When I Whistle?
A framing narrative is a term that is given to a story-within-a-story, or, to use the analogy of framing, a central story that is "framed" by an outer story. In such tales, the framing story begins, and then the central story is told, before returning to the framing story and its conclusion. In such tales there can often be several stories nestled within each other like Russian dolls. Good examples of framing narratives are Frankenstein and Wuthering Heights.
This novel by Endo does not use a framing narrative. Rather, it elaborates on the theme of the differences in understanding between the generations in post-war Japan through an alternating chapter focus, with chapters in turn focusing on Ozu, who grew up in Japan before and during the war, and Eiichi, his rather opportunistic son, who represents the younger generation that has lost something of the sacredness of life in their materialistic approach to work and existence. Note how Ozu's wife tries to defend their son but also identifies the different values that exist between the generations:
Times are different... Young people now can’t survive if they don’t push others out of their way. There’s really nothing else Eiichi can do.
The structure of this novel therefore gives voice to these two differing perspectives through its alternating focus on both of these main characters, and their contrasting world views. Endo does not employ a framing narrative in this novel to elaborate the central theme.