Marley is about 2 years old.  Recently he makes this weird goose like honking noise when he see another dog mostly bigger in size.  He gets excited and darts towards the dog and barks, a kinda of territorial type of bark.  As I pull him away on the leash (light tug) he makes this goose like honking noise and starts choking and at times hacks out liquid (not white but clear).  This only happens if he feels threaten by other dogs.  When I take him out for long walks or play fetch none of the problems mention above occurs.  It only occurs when he sees other possible threatening dogs.  He has no problem breathing after running for long periods of time.  Marley also eats and plays normally. 

Ive looked up the symptoms Marley has and only came up with Kennel Cough (i doubt it is), Tracheal collapse and Tracheal infection. 

Anyone else experienced the same things with their corgi or other breed of dogs?  If so what exactly is it and should I take him to my bet and get an x-ray?

Thanks