2002 Wrangler with 3.0 6 cyl making ticking noise??

I have been doing maintenance for my cousing who has a 2002 wrangler with 6 cyl, automatic 65,000 miles to date. I have done 3 oil changes for her-at the recomended intervals- using synthetic and new filters and air filters each time as well. Last one I did about 6 months ago. She has had a ticking noise recently that developed after the last oil change(not sure how many miles after but approx 2 months after the change). Yesterday we went for a test drive; starts normally no ticking for several miles but then after fully warmed up and 20 minutes of driving a ticking developed and really became noticeabler in the driveway. Popped the hood and sounds a LOT like an exaust leak tick -like you get with header gasket leaks but could be comming from valve cover as well, took off the oil fill cap and it didnt get any louder??? When you rev the engine it follows RPM and gets louder as the rpms come down after letting off??? What are the main possibilities here? Exaust gakset leak was my first impression, but could be a intake gasket leak-is that common on these engines?, or a sticking valve or lifter? Oil pressure is good-40 PSI hot. I am stumped. Fuel injector going bad??? Thanks for any help.

cracked exhaust manifold. real common promblem.