If they could, then isn't that suggesting that the talk isn't a "physical" thing? Talking requires air passing across / through a voicebox and I wouldn't think a ghost would actually have a physical voicebox nor would be able to directly influence something physical like "air" to a degree that it could warble their voicebox if they had one ..
The stone-tape is an interesting angle I suppose. But for those people who have heard distinct voices in response to a question - wouldn't the words spoken need to have been recorded? I've heard a direct response to a question - ok, it was a simple "What?" - but wouldn't that word needed to have been recorded at some point and then, some "intelligence" required to replay that particular response at the "right" time?
I don't know. Theres a bit of confusion here with me. I've heard a voice, but I can't figure out the "how" part of it ..

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