“Cuando el río suena, agua lleva” comes from Spanish culture. There’s also another version of the same proverb, that is “cuando el río suena, piedras trae”, but in English the translation is always the same: “Where there’s smoke, there’s fire”.
This proverb means that rumors can be founded sometimes, and so you have to be careful. In other words, it tells us that every sign can prospect a real fact; in a more popular sense, it asserts that whenever you speak specifically about someone, that’s why because there’s something real, and not just for invention or myth.