IDIOMS

rumor mill

(idiomatic) A group or network of persons who originate or promulgate gossip and other unsubstantiated claims.

Example: 1963, "A Kennedy Speaks to a Lodge," Time, 5 Jul.,
  For months the Washington rumor mill has ground out gossip about who might replace U.S. Ambassador Frederick E. Nolting Jr.
2008, "Zimbabwe Opposition Claims Victory," New York Times, 30 Mar. (retrieved 19 Sep. 2008),
  Unofficial results instead traveled through the rumor mill, passed along on mobile phones from one part of the country to another.