Got a TJ 2.5 with about 75k mi. and have a rapping noise which starts about 30 seconds after a startup. Using Mobil 1 10-30. I've replaced the lifters, pushrods and rod bearings, replaced end bolts on the exhaust manifold. The noise hasn't gone away and maybe is a bit louder. Last nite I pulled off the ccv hose to the air box. When I held my thumb over the elbow on the valve cover as the vacuum pull on my thumb increased the rap went away.
When I removed my thumb the rap gradually came back. I flushed the engine with Gunk cleaner and the rap is still there. Any help or ideas would be appreciated.