Hear something over (throught) the grapevine.

　　A traveller's tale.

　　eg：I hear over the grapevine that you are moving to Shanghai.

　　中英俚语俗语来源：论语·阳货：“道听而途说，德之弃也。”

　　同义词：街谈巷议 Way-side inn gossips.

　　反义词：言之凿凿 Straight from the horse's mouth.