"05" Ranger Clackity Clack

I have a metalic clacking noise that is definately coming from underneath my Ranger and seems to be from more towards the rear of the truck. It is an automatic and I am nearing the end of my warranty. It has been to the dealer 4 times and they have re-riveted the heat shield on the converter to no avail. Still clacking. The biggest rpoblem is that it happens mainly when the truck is cold and with the weather warming up I am afraid that it will not be able to be detected until next winter when my warranty will of course be over.