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I heard about it through the grapevine.
Literal
Wind [possessive-の] message [with-に] heard.
風の便り (かぜのたより, 'a message on the wind') is a beautiful idiom meaning 'heard through the grapevine, heard indirectly.' The metaphor of news carried by the wind captures the indirect, untraceable nature of rumor and hearsay. A compact, poetic sentence.