get some hydraulic lifter cleaner (forte or wynns i think) and try that to c if it makes a difference.

If its just when the engine is cold, dont worry to much. The owners manual tells u that a cossie engine (2wd...duno about 4x4)will tap from cold because of the forged pistons (sorry, pissed and cant member all details.....read it in owners guide a when i bought mine)