well, the clicing is probably they way they talk with each other, can also be to to scare theyr prey (or a predator that hunts them from theyr home planet, the clicking can be a very loud sound for some animals)
they must make some sound dont you think?
just because they cna copy what humans say i dont think they use some language like that to comunicate with each other (like stuff from comics where they call themselfs yautja...i havent seen those comics but if they call themselfs yautja it certainly isnt by clicking)