The earlier Gen3 V8s (97-01) may exhibit what engineers call "cold piston knock" and what laypeople may call "piston slap". A "normal" instance of cold piston knock will produce a "ticking" or "clicking" sound which is very much like what you may hear from injectors or rocker arms but the noise will reduce in loudness then go away shortly after start up.
In 2002, changes in block machining and the addition of piston skirt coatings reduced instances of this problem.
Case of cold piston knock as described above are merely an annoyance to some but pose no reliabiilty/durabiilty problem.
That said, if the noise is very loud or it persists as the engine reaches operating temperature, there might be a problem with the engine, ie: "excessive" piston knock or some other issue which causes noise.