Help: Loud ticking upon very cold startup

When my 01 Xj sits for a while 10+ hours or longer when you start it there is a very loud ticking coming from the engine. It doesn't happen all the time, but on a weekly occasion. When the engine warms up after about 3-5 minutes, its completely gone. The car drives fine and runs like normal. It almost sounds like a slapping rod or an exhaust leak. Anyone have any experience with this?:banghead:

btw i have had the head replaced around 5k miles ago, milled new gasket etc

Sounds like a stuck lifter. Not pumping up fast enough. Mine does it cold for about 15 seconds on #5 or 6, I can't tell but NEVER for minutes like you're saying.
Run some Marvel Mystery Oil in the oil and some Mopar Combustion Chamber Cleaner for good measure to get rid of carbon.
If it's ticking for a few minutes already, get on it now before you get a collapsed valve. I'd probably Pop the VC off and torque check the rockers/inspect lifter/springs if ya can and clean any gunk that may be in there.