I've heard various opinions from lay-people if a woman's whistling and/or humming a tune are considered kol isha, which a man shouldn't listen to, and something women should be considerate of. I looked at some contemporary seforim (for example Halichos Bas Yisroel) but they didn't discuss it. Are there any halacha seforim or known opinions of poskim which discuss this?
(I wouldn't necessarily call this a tsnius issue but I don't know of a better tag)
