The Gong emits a sound like the frightened scream of a helpless baby Glute. The Knaarens, who're always keen to punish the little ones, can't resist its call.—Official description, Rayman 3: Hoodlum Havoc
A gong is an instrument found in the tunnels beneath the Desert of the Knaaren. When hit with a Shock Rocket, the gong makes a sound that imitates a frightened scream of a helpless baby Glute. The Knaaren that dwell in the tunnels are unable to resist this noise and immediately run towards the gong to find the baby and punish it. This gives Rayman a chance to run past the distracted Knaaren and enter the next part of the level.
In Rayman Origins, several gongs can be found in the The Desert of Didgeridoos. When characters hit a smiley gong, it creates a circular sound wave, driving away dense swarms of bugs and temporarily opening up paths which can then be traversed. When characters hit a cyclops gong, it creates a particular circular sound wave that moves around with the characer who played it, and slowly gets smaller until time is over and the character is exposed to bugs again.