hear (something) on the grapevine
To hear or learn of something through an informal means of communication, especially gossip. I heard on the grapevine that Stacy and Mark are getting a divorce. A: "How do you know the company is going bust?" B: "I heard it on the grapevine."
hear something on the grapevine
acquire information by rumour or by unofficial communication. This phrase comes originally from an American Civil War expression, when news was said to be passed ‘by grapevine telegraph’. Compare with bush telegraph (at telegraph).