Thats funny mine does this too, not all the time but often enough for me to think "WTF " ?
The engine feels strong as an OX & can easily drag off TJ's & XJ's ect so I dont think too much off it. When i've been driving for a while it stops, but sometimes it stays for ages. I've done 7000klm and am about to change the oil for the 2nd time. I did the first change at 1500klm as I do this regardless of what a dealer tells me (on every car i've owned since new). I spend alot of the time in dusty conditions so changing the oil is something I do regulary and the airfilter for that matter.
I've just bought a new 15W40 turbo oil from PM Lubricants. They are famous in Australia for the trucking industry. They get much better (less) engine wear, better power & fuel economy, and bearings ect last alot longer. I've been told it will quieten the engine down a bit too, as the Mobil 1 that's in there is a 0W30 - too 'light' for such a tight new engine, and will shear quicker. OK for running it in for a few months, but time to change to the good stuff
IT was either that or Redline, something i've used in my performance cars on the race track & road.
Just place one end of the rod on suspect area of noise emission, and hold the other end to your ear and move rod around till you find location of noise. The actual stethoscope is going to be lots better but you may be able to point the parts changers in the right direction just using the home-made jobber.