What does "Whistle your soup" mean?

Factual Questions
#1

Reading a book published in US in 1930’s. Contains line “If you whistle your soup, you may be looked at queerly…”

I’ve tried a bit of searching in online dictionaries of phrases without help. I suspect it means to make a noise or blow soup out of the bowl while blowing on it to cool it (and thereby being gauche). Close?

#2

Don’t know for sure, sorry. WAG: to “whistle” soup might be to blow it cool by the spoonful.

There’s a record of a Disney track called “Whistle Soup”. Any connection?

#3

It probably means the loud sucking sound people make when sipping slowly from their spoon. Like the dinner scene in “Clue.”