Shouldn't it be "słyszymy Głosów"? Isn't genitive always requiered with słyszać?
No. "słyszeć" (to hear) takes Accusative, "słuchać" (to listen to) takes Genitive.
As far as I remember there was a post with a small list of verbs and cases they take that you or immery shared with someone in comments. Is it possible for you to share it with me, please?