It may be TMJD which is Temprolmandibular joint disorder. it usually has something to do with the muscles in the dogs jaw. the same thing happens with humans. it can be fixed if it is TMJD by massage. you may want to take your dog to the vet and let them know about the clicking. they may take xrays to find out if the jaw is coming unhinged or if there is extra bone in there. if they cant find anything then it may by TMJD.