Hello, And Welcome to Just Answers. We use a procedure to located exhaust leaks. This will detect very small leaks that can cause check engine light complaint on the newest vehicles. We have built a rubber cone that fits into the exhaust pipe and plumbed into the cone a air line that has a pressure gauge and regulator . We adjust air pressure to be no more than 5 psi. We use liquid soap and water in a spray bottle to locate the leaks. Some times on large leaks we need to reduce the air pressure to allow bubbles to form.
We normally find that exhaust leaks disappear after the engine is warmed up. So this method will not work on a hot engine, it just steams off. We also can use a smoke generating machine to look for leaks , But its hard to get the smoke past the hot catalytic converter- So we put this smoke into the intake and wait untill it starts coming out the exhaust before we plug the rear pipe. We wrap plastic around the throttle body opening to seal it, You will be surprised by the vacuum leaks.
I also need to mention my first thought on this problem. You may have a valve train noise caused by a spring or seat, the MDS system- if equipped will be also working at this time too. It turns off some cylinders at certain times , An aftermarket exhaust will allow you to hear the cylinders go in and out easily . Any heavyline Dodge mechanic will be able to tell you if that noise is valve train noise or not. Thanks . Scott