Wacky Sound Effect

A "wrong" sound effect that doesn't fit the action portrayed is played for comedic effect. This is for the audience's ears only, the characters never notice in-universe (that would be Sound Defect).

On some shows, this is done routinely and serves to enhance the overall wackiness, on others it is used sparingly and to make a specific auditive point or gag, for example when the impact of a huge object fails to produce the ear-shattering KABOOM sound the audience expects. Typically, 'big' things get a 'small' or silly sound, but the trope works the other way around as well. Stock Sound Effects and inherently funny sounds (associated with circuses and clowns) are especially popular. In a common variation, this trope is Exaggerated by the use of a different Wacky Sound Effect every time an action is repeated, for example when a character is repeatedly hit on the head with the same object.

Sometimes, a sound is played where there shouldn't be anything to hear, for example Squeaky Eyes (a subtrope). Contrast with Audible Sharpness and Audible Gleam which aren't considered wacky but rather cross over to Coconut Effect territory. Contrast also with Space Is Noisy, where 1) the space noise is also more or less expected by the viewer and 2) the sound effects are pseudorealistic rather than wacky. See also Editorial Synaesthesia.

Another extreme version of this is when something or someone gets a sound effect for just being there or coming into view.

Wacky sound effects are a staple of animation, but also sometimes used in older live-action works where it is likely, however, to be deemed by a present-day audience to feel inappropriate and tantamount to Special Effects Failure. Then, there's the connection to Slapstick and, by association, to funny home videos.

Film

 * The Man with the Golden Gun features a visually impressive Ramp Jump car stunt which is accompanied by a silly cartoony slide-whistle sound.
 * Many fans were very upset that one of the most spectacular car stunts in film history was essentially ruined this way, effectively sabotaging the entire chase scene of which the stunt was part. The scene is thus often considered to symbolize everything that many considered wrong about the 1970's Bond films.
 * In Star Trek III: The Search For Spock, the sabotaged U.S.S. Excelsior's engines fail with a sound effect that resembles a stalling car.
 * In the movie Airplane!, this was coupled with Just Plane Wrong as in-flight shots outside the airliner were accompanied by the sound effect of prop aircraft.
 * Not to mention the sound of a steam locomotive as it pulled away from the airport terminal.
 * In Mom and Dad Save The World, two guards, on orders from Spengo, shoot themselves in the head for their stupidity (they gave him a opinion on facial hair that he did not like). When the do this with their quirky ray guns, one can hear what sounds like a rubber duck being squeezed.
 * In Repo! The Genetic Opera, during the song "Thankless Job", several wacky sound effects can be heard.

Video Games

 * Joke weapons in Soul Calibur II produce Wacky Sound Effects every time they connect: Astaroth's Rock trumpets like an elephant, Yoshimitsu's Shepherd's Crook bleats like a sheep, Necrid's Ethereal Edge makes a "boi-oi-oing" noise, Nightmare's Galley Oar makes a sound like breaking waves, and so on.
 * The weapons in Worms games sound wacky - because they are.

Web Original

 * In a Garry's Mod video called "Mass Defect" created by Kitty0706 involves one of two 'fancy' Servant Grunts from Amnesia the Dark Descent saying "Fregley, get into character quick!". Immediately afterward, a Wacky Sound Effect along the lines of "BAP" plays, they lose their top hats and monocoles, and they proceed to growl like zombies and chase after the 'protagonist'. Link: http://www.youtube.com/watch?v=V 46 K Yx Fav 24

Western Animation

 * Invader Zim had this in spades.
 * Done regularly in Looney Tunes cartoons - a gunshot sound for a slamming door, for instance.
 * SpongeBob SquarePants has lots of illustrative sound effects to enhance the physicality of the characters: SpongeBob has both 'woody' (when his arms break off) and 'spongy' (when he walks) sound effects. Also, his facial expressions are quite noisy.
 * All spaceships in Futurama seem to be fitted with horns.
 * Drawn Together has lots of these, with Wooldoor Sockbat as the epicenter. His masturbation technique involves a long string of Wacky Sound Effects.