rumour campaign
A concentrated and prolonged effort to damage or ruin someone's or some group's reputation through the perpetuation of rumours, innuendos, and/or falsities, generally as a means of persuading a large amount of people against him, her, or them. Primarily heard in UK. Finding himself at the wrong end of a vicious rumour campaign, the local MP's slim lead heading into the election quickly evaporated. I think we need to start a rumour campaign to slow down the competitor's growth in the market, but no one can know that it's coming from us!
rumour mill
The source from or process by which rumours are generated, spread, and perpetuated among a group of people. Primarily heard in UK. Listen, Barry, you can't believe everything that comes out of the rumour mill. I can guarantee you that there will be no redundancies this year. One of the downsides of gaining celebrity status is having every aspect of your life subjected to the Hollywood rumour mill.