Chrysler pacifica tapping noise

I have a Chrysler pacifica 2006 .Later in 2009 I had a problem ( ‘tapping noise’ coming from the engine). I took the car to the dealer, since at that time I still have warranty (39,000 miles). They changed: 18 arms (6 of each type) 8 dowel pin, belt and the lifters. Last year I started hearing the same noise again. The car was with 56,000 miles. I thought it should be under the warranty (service done), but it wasn’t. So I decided to have the dealership servicing the repair. This time the part changed was only one. The receipt says they changed the ‘arm-inlet and exhaust valve’. Guess what ? the noise still there and they say they won’t open the car without me paying for the diagnosis ( many hour of labor for sure!).
What can I do?

Has the oil been changed regularly on this vehicle?