Need assistance/reasurance from the knowledge base.

In the last week or so I've noticed that when I shift into PARK my engine idle seems to stumble for a second or so. Now this is my first vehicle with an automatic transmission and this is the first I'm noticing this after owning/driving my 2001 Explorer Sport Trac, so I'm unsure if it is an issue. I've scanned for any codes and none have come up so I'm at a loss and concerned.

Could this be a symptom of a potential serious problem?
Could this be a transmission issue? An engine idle issue?

Thanks for the assist.