услышать по сарафанному радио (An indication that a piece of information (not always reliable) was obtained via an informal contact with a person who was told it by someone else. Wakeful dormouse); за что купил, за то продаю (Wakeful dormouse)

hear something/about something on the grapevine

до кого-либо дошел слух (DrMorbid)

hear on the grapevine