Clakking

A secret language spoken by Clakkers by using their gears to produce precise and specific clicks, ticks, clangs, etc. It is almost impossible to distinguish between these special sounds and the sounds constantly being generated by their bodies. There is no written form of Clakking.
A Clakker or person trained in Clakking can always distinguish between these sounds without having to make a check. Someone who is not trained in Clakking, but is aware of the language, must make a DC 25 Linguistics check determine if Clakking is being spoken. Someone who is unaware of Clakking must make a DC 40 Linguistics check to realize a language is being spoken. Your GM might require a perception check before the linguistics check to determine if you can sufficiently hear the sounds being made by the Clakker.
A non-mechanical body can never hope to reproduce the rapid and precise sounds of Clakking and as such cannot effectively reproduce the language, even if they understand it.