my experince is a rocker ticking and an exhaust leak sound close.
as vertstang stated check for soot or air pulses around manifold.hedder gaskets are notorious to leak. also check where the exhaust pipe connects to hedder or manifold whatever the case may be.may be just loose bolts there.to find out if rocker, i use a mechanics stethoscope .you can pick them up at autozone on the cheap. or my dad used to use a broom handle lol and put it to ear and engine.the stethoscope really workswell on locating noises in motor. if it is from a rocker have to pull valve cover check them for tightness if tight then maybe a pushrod slightly bent , lifter collapsing, or worse case cam lobe wiping , but u said motor runs fine so i suspect it is going to be an exhaust leak . good luck on finding it. lets us know what ya find.