Tongue is a muscular organ and so no clicking sound can come out it. It may be due to habit. The clicking sound can come from TMJ which is tempromandibular joint. when we talk this joint is responsible for movement of the mandible. If you had some sort of trauma or infection which causes dislocation of this joint, then this sort of sound is possible. You can visit a dentist and discuss because without detailed history, clinical examination and xrays it is not possible to diagnose it. For more info you can read this article... http://www.identalhub.com/dental-what-is-the-problem-of-popping-jaws-722.aspx