The author is characterizing the speaker as someone who is trying to come off as representing a larger group (perhaps the household in question) but failing at that, and who is to the author's ear someone who is prudish and self-righteous. It could be someone's grandmother venting her disapproval of what she feels are the somewhat loose morals of the people upstairs from her. The "wannabe voice-of-the-people" description implies that the speaker wants her chastisement to carry more than the simple moral weight of one person's opinion: she wishes to imply that all right-thinking people would share her outrage.
I use "she" to characterize the speaker here because the author uses "shrill" and "virginal" in the description, two adjectives which are not normally applied to men (although they could be, in which case the author would be putting the speaker's manhood in question as well).
Edit: In case you don't know, "wannabe" is a contraction of "want to be" and can be used as an adjective, as here, or as a noun. It implies someone who purports or wishes or pretends to be someone or something he or she is not. It is used as a put-down, in sentences like "Most waiters in Manhattan are wannabe Broadway stars." Such a waiter would be someone who, when asked his occupation, would give it as actor, even though he works 40 hours a week at the restaurant and has never made a dime from acting.