Well if it is a tick, look up "HEMI tick" and you might realize it is a broken bolt on the exhaust manifold (typically passenger side, rear bolt) allowing exhaust gas to escape/leak. Just did mine this weekend and if you're "lucky" is very obvious as the sheared off stud under the bolt head you can identify if that is the case by simply pushing on the heat shield and it will readily move indicating the underside of the stud snapped. Mine was the rear stud on the passenger side of the exhaust manifold. The entire cast iron manifold was warped pretty bad (1/8" from front to back) and likely would recur. Assuming the warping was thermally set in, used angle grinder to smooth out the difference (from about 1/8" down to maybe a 1/32" to 1/16" and with new gasket is performing well again. Alternatively consider new headers as this is an overall bad design if that warped. My truck has 75,500 miles on it so out of warranty.