unfortunately i had the same or similar noise in the last liberty i had and it died the death of blown head gasket which will also give you that nice ticking sound under load.
This may not be the case with your car but for the sake of saving a liberty i would check and keep your eye on the    water level just in case.
fingers crossed it is a shitty manifold gasket somewhere mate.

go back to exhaust shop and get leak test done, especially around headers.
if that all comes back clear, get a long screwdriver, place it on each head/valve cover and stick your ear on the handle, you should be able to hear the ticking resonate through the screwdriver if its lifters.. if so, go to Bursons and get some Nulon Lifter free (ask for TRADE STRENGTH) only Bursons sell it, the usual repco or supercheap will only have retail stuff.

i cant remember if its before or after an oil change but the EJ22's get a bit ticky when the oil is old, and also, the nulon stuff works wonders!