I noticed yesterday that I have a rattling/clanking noise under my drivers side floorboard when the truck is in park at an idle. When I rev the motor the noise/vibration seems to go away. There seems to be no noise in the other gears at idle though. Is this a sign of the tranny beginnning to crap out or what? Any info would be appreciated. BTW the truck only has 49,800 miles on it. 2001 5.9L 4x4 ext cab.

 

Sounds like something is loose under there. Crawl under and locate before something comes off.

The other day someone had the linkage for the 4X coming loose

 

My '01 does the same thing.
Not very loud, but loud enough to notice.
Haven't found it yet. Mine goes away when I push on the brake pedal!!!
I HATE NOISES!
If you find it let me know.
I've just been living with it.

 

Sounds like you probably have something loose under there, maybe some type of hose of some sort.