German radio production and tutorial website Benztown recently took to the Stuttgart Airport to record some SFX, which presented various issues such as clipping, noise and hum. iZotope RX 3 was employed to clean up these issues and the results are posted in an english-language review with audio samples here.
(Tip: be sure to listen to the audio samples through quality headphones or studio monitors - computer speakers won't cut it for this precise work!)