Hemi Tick
I too have the "Hemi Tick" too on my 88,000+ mile 5.7L Hemi. I think it is a combination of several things.
1. The lifters are set high in the block as compared to other V-configuration engines in order to fit the push rods in at a suitable angle to the rocker arms (and still have long term durability), the lifters and cam are set high and that leaves less engine mass to dampen lifter noise.
2. The MSDS solenoid lifter assemblies are known to be a little noisier than the no MSDS Hemis (trucks 2003-2005). MAKE SURE you only use 5W-20 synthietic or synthetic blend oil (high quality). Heavier oils cause the tightly toleranced solenoid-lifter assemblies to bind a little and "click". If you've had 5W-30 installed, as my dealer did once, it shouldn't cause permanent damage.
3. If there was more sound deadener, the noise would be less notcieable. NOTE: the engine cover is not just for a clean underhood look, it has foam on its underside to act as a sound deadener.
Another click heard under heavy acceleration is a small valve mounted on the firewall that is a part of the evaporative recovery (EVAP) system. This is a plastic (nylon?) solenoid type valve that opens and closes as the engine operates. It has no insulation around it and being plastic, it has little mass to absorb its own sound, etc.
In any event, my engine has run beautifully and has been maintained properly. I don't think the "tick" noise is anything but normal for this engine.