through the grapevine
Through or via an informal means of communication or information, especially gossip. There is always some absurd rumor or piece of misinformation through the grapevine at work, but I try to just tune most of that out. I heard through the grapevine that John is planning to propose to Samantha next week!
on/through the ˈgrapevine
by talking in an informal way to other people: I heard on the grapevine that you’re leaving.