Did you ever wonder what's causing that ticking sound after your engine is shut off? The answer is two words- metal expansion and contraction (during the cool down process). The sound can come from a variety of sources, such as the heat shielding around the exhaust, the exhaust pipes, the catalytic convertors, the stainless "clamshells" around the SRT shorty headers, the 5.7's cast iron manifolds, etc. You'd be surprised how much an exhaust system "grows" in length as it heats up to operating temperature. When the system is being designed, there's some compensation to allow for the lengthening of the exhaust to insure there's adequate clearance and the hangers are spaced to allow for that.