I listened to Chicago’s Chicago II this morning. In both “P.M. Mourning” and “Memories of Love” - although it’s more clear in “P.M. Mourning” - there’s this flute part. It’s three ascending phrases, ending in some shriller tones.
It sounds almost the same as the whistle that Willy Wonka plays to get the attention of the Oompa Loompas in Willy Wonka and the Chocolate Factory. The movie is from 1971, and this album is from 1970, so it is possible that the Willy Wonka and the Chocolate Factory people took that phrase from this album. I’m not sure how likely it is, but they do sound pretty similar. (Though I feel I must admit that it’s been a few years since I’ve last seen Willy Wonka and the Chocolate Factory.)