I know that XJ headers are prone to crack at the collector, but I've got a 2000 with the two-piece manifold and as far as I know these don't have the cracking problem like the earlier one piece style. Is this correct? I have some sort of exhaust leak that I can hear up under the engine and you notice it a little (not every loud) while accelerating round town, or when the windows are up you can hear it through the firewall. I've visually inspected for cracks (all that I can see by crawling underneath and removing the airbox up top, but can't find any cracks. Is it common got the gasket(s) between the manifolds and midpipe to start leaking. It's done this pretty much since I got it if I remember right, and I replaced the head not long after getting the thing so the manifold gasket has been replaced. I'm stumped at the moment. I don't really want to pull the intake manifold off just to do a more thorough inspection until I can reasonably narrow down the source of the noise. Any thoughts?

 

Cold engine, spray bottle of soapy water...look for bubbles. Once the manifold heats up the water won't stay long, lol...gotta work fast.

 

I have the same problem unfortunately. Mine is a slight tick that gets faster from idle until 1300 rpms and disappears. Mines not the evap valve either.
My jeep is a 99 though.