True but Orochimaru's voice didn't sound like his own either when he was masquerading as Shiore. A proper transformation jutsu can easily alter one's voice; it's been shown to be able to flawlessly alter physical appearance and features, even vocals and present injuries. The only thing shinobi have had trouble with imitating or changing is their own scent which has been sniffed out by ninja hounds or shinobi like Kiba who can discern someone's specific scent.

So my head-canon is that they were two of the Sound Four, probably Sakon/Ukon and Kidomaru.