Weird scary noise

So I checked my oil today, levels are fine on my 4.0 straight six 90 cherokee. I get to school and I'm sitting there idling and I know notice this strange ticking noise as I'm sitting there, it sounds like my engine is starting to develop a slight knock, this tick increased as I gave the engine gas.I shut the engine off and started it back up and gave it gas the noise was still there and then it went away. What could this be, it was 52 degrees outside, I changed the oil 2,000 miles ago, but did not change the filter, because the filter I got had an oring problem, so I lost all of my oil. So I just reused the old filter which is a wix, and got mobil 5000 oil 10w30. So what should I do now, is my engine slowly on its way to death. IT does have piston slap, and an exhaust manifold leak, but I have to say that I cannot attribute this morning's noise to that leak.

My valves tick until the Jeep warms up; I wouldn't worry.