I was always under the impression that Harry's Parseltongue talent came from his brush with Voldemort, so I like to entertain the idea that Ginny possibly gained the talent after her first year at school and her rather... close connection with Tom Riddle (y'know, the whole "sucking the life force out of you" thing could have gone back the other way when Harry stabbed the diary, thus transferring some of his talents back to Ginny).

But yeah, it defies all real reality about snake's hearing, so I think there's an extremely strong magic component to it, which is why Ginny is a possibility with me.