HLA - hydraulic lifter assembly.
They're your lifters, and to the person asking about adjusting them : you can't adjust the backlash on hydraulic lifters.
They fill up with oil (like balloons) and ride the lobes of the camshafts, and the ticking is heard whenever they don't completely fill with oil.
Instead of riding the lobes, they slap up against them, causing the ticking.
Synthetic oil helps, and so do "oil flushes" with kerosene or bottled oil flush additives. The flushes clean the pathways to the lifters, and the synthetic keeps from leaving as much gunk to block them up again. Thus, better oil flow.
An oil filter with an "anti-drainback" valve helps as well so that the oil can reach the top of the engine faster (where the lifters are) on cold start ups.
Some people have problems, so don't.
The only permanent solution is the revised oil pump previously mentioned, but changing oil & filters solves the problem for some, provided you stay with that regime.