I did an oil change tonight, used rotella 5w40 just like last time, only this time I used a Donaldson oil filter instead of a lower end napa oil filter and took it out for a drive. My warm idle engine tick is now a bit louder and also seems to be now irregular at times. I did some investigating and it seems to be coming from around the exhaust manifold. I read that sometimes the cat converters going bad can cause a rattle, but would something like that go away at 1500 Rpms like mine does? Also, if the cats go, how do you test that, and wouldn't you be thowing codes?
I am totally stumped and would figure fresh oil would help things, and all my investigating got me was a nice burn on my arm while crawling out from under the truck.

 

I had that happen once, actually the oil change briefly started a tick. I had gone to the high end Fram just to try it. Swapped out the filter immediately after hearing different rumblings than I was used to in the engine. It quieted back down with KM 301. And I'm assuming you mean 15/40 Rotella? Also make sure you fill up the filter with oil before you screw it back on. It's messy but it saves the pump from running dry those couple seconds and it is what is recommended in the manual. If changing to another filter doesn't clear it up it's possible one of the lifters didn't fill after the change or got clogged in which case you will get a few suggestions from this crowd as to how to fix that. The one that worked for me was to quickly do an oil change (when warm) then restart and rev it very quickly to around 3k or more (preferably driving it if you can) for about 5 minutes. This solved my intermittent warm tick and it has never come back. I found this technique on an aussie LR forum. Can't find the link, but it worked for me.

 

It is quiet possible the tick you are hearing is coming from the exhaust manifold and a leak there. I know someone recently here changed that out and took care of the problem. The tick might still be there and internal, but you don't hear it unmuffled. I don't think the cat going bad would make a tick though...a rattle yes. If you smell a rotten egg smell from the exhaust, that is usually the sign of a bad cat.
As far as the oil goes, new and thick oil (oil sheers down and gets thinner as you go; more likely in regular vs syn) could be harder to pump around and get to spots, as well as flow through clogged passages. So, it isn't all that crazy to think fresh oil could cause that. I wouldn't think the actual filter would have all that much to do with it though. A better filter will have more filtering, so could be less flow, but those usually also have more surface area so that should not be the case.

 

If it is an internal tick, and because it is an 03, I would first do a oil pressure test, stone cols at idle and 2000 RPM/s and at operating temp. at idle and at 2000 RPM's then back to us. If the pressures are good, then before you cost yourself some large repairs, it is time to pull the valve train down for a complete inspection, noise means damage means $$$$$'s.
I would also get away from 5W oils and go toward a 15 W/40.