Once in the Warring States Period, the State of Jin was at war with the State of Chu. Duke Gong of Chu stood on a high platform built on chariot and watched the movements of the Jin army. After watching for a while, he said ,"It"s quite noisy over there and cloud of dust has been stirred up." His aide answered, "The enemy are filling up wells and destroying their cooking stoves. They are preparring to fight."
This idiom is now used to mean a lot of commotion over hearsay.