During the Warring States Period, the State of Jin was at war with the State of Chu. Duke Gong of Chu stood on a high observation platform mounted on a chariot and watched the movements of the Jin army. After a while, he remarked, "It's quite noisy over there, and a cloud of dust has been stirred up." His aide replied, "The enemy is filling up wells and destroying their cooking stoves. They are preparing for battle."
This idiom is now used to describe a situation where there is a great deal of commotion or fuss stirred up over mere hearsay or rumors.