Sing! Or don't, it might be Assur.

Rabbi Yitzḥak stated: An exposed handbreadth in a woman constitutes nakedness. The Gemara asks: Regarding which halakha was this said? If you say that it comes to prohibit looking at an exposed handbreadth in her, didn’t Rav Sheshet say: Why did the verse enumerate “anklets and bracelets, rings, earrings and girdles” (Numbers 31:50), jewelry that is worn externally, over her clothing, e.g., bracelets, together with jewelry worn internally, beneath her clothing, near her nakedness, e.g., girdles? This was to tell you: Anyone who gazes upon a woman’s little finger is considered as if he gazed upon her naked genitals, for if his intentions are impure, it makes no difference where he looks or how much is exposed; even less than a handbreadth. Rather, it is referring even to his wife, with regard to the recitation of Shema. One may not recite Shema before an exposed handbreadth of his wife. Along these lines, Rav Ḥisda said: Even a woman’s exposed leg is considered nakedness, as it is stated: “Uncover the leg and pass through the rivers” (Isaiah 47:2), and it is written in the following verse: “Your nakedness shall be revealed and your shame shall be seen” (Isaiah 47:3). Shmuel further stated: A woman’s singing voice is considered nakedness, which he derives from the praise accorded a woman’s voice, as it is stated: “Sweet is your voice and your countenance is alluring” (Song of Songs 2:14). Similarly, Rav Sheshet stated: Even a woman’s hair is considered nakedness, for it too is praised, as it is written: “Your hair is like a flock of goats, trailing down from Mount Gilead” (Song of Songs 4:1).

A Woman's Thigh is Erva: This teaches us that even if at times it is revealed, it is like a concealed place because it leads to Erva. A Woman's Voice is Erva: This is for matters of Kriat Shema. And some people say that this is regarding a singing voice and hair which is normally covered, but regarding a voice which is not a singing voice, and hair which is out of a braid, we are not concerned

A person must stay very far from women. He is forbidden to signal with his hands or his feet, or to hint with his eyes, to one of the "arayot". He is forbidden to be playful with her, to be frivolous in front of her, or to look upon her beauty...It is forbidden to listen to the voice of an erva or to look at her hair. If one intentionally does one of these things, we give him lashes of rebellion. These things are also forbidden in the case of ordinary Biblical prohibitions.

The hair of a woman that it is her practice (lit. way) to cover is forbidden to recite [the Recitation of the Sh'ma] in front of it. Gloss: even his wife . But unmarried women for whom it is their way to go with an uncovered head, it is permitted. Gloss: And so too is the law with the hairs of women that regularly come out of their covering (Beit Yosef in the name of Rashba) and certainly foreign hair [i.e. a wig] even if it is her practice to cover (Hagahot Alfasi haChadashim). 3: One should be careful from hearing a woman's singing voice at the time of the Recitation of the Sh'ma. Gloss: And even with his wife. But the voice to which one is accustomed has no [element of] nakedness in it. (Beit Yosef in the name of the name of Ohel Moed and the G"M)

Everything which is written in Shir HaShirim, one must be cautious with, [for example] that he must not hear the voice of a woman, and the same goes for a woman, that she must not hear the voice of a man.

And the reason it seems that there was no concern regarding a woman reading megillah....is because that which is said in Masekhet Berakhot...is clearly said in Sepher Yere'im, a voice of song, so is it in the Mordekhai and in the Rishonim...and this is how it is brought as Halakha in Orach Haim....And according to all the Rishonim, the singing of the Trope of torah reading is not considered song...and this is what the Kaf haHayim brought.