Potential fix In some cases, this issue can be resolved by clearing audio caches. This can be easily accomplished with a tool like OnyX.
In other cases, resetting PRAM/NVRAM can resolve the issue. In order to reset PRAM/NVRAM, shut down your Mac, then start it back up while immediately holding the following keys: Command, Option, P and R. Hold the keys down until the computer restarts and you hear the startup sound for the third time.
In still other cases, this issue can only be resolved via authorized Apple repair. Contact Apple support or bring your MacBook Air to a local Apple retail store for assistance.