On my 2001 7.3 6 spd, there is a chatter or rattle noise when the truck is running, but goes away when the clutch is pushed in (?)

 

Mine was like that too, I wouldn't worry about to much. How many miles? My clutch looked decent when I changed it at 200k.

 

Same here..wish I took pics to post up, but with trans divorced, the input bearing was gone, throwiut hanging on by a needle, chips in the clutches...etc. Can't believe it actually/somewhat still worked.
. With new parts and clutch, the clutch is very soft and smooth and NO noise...i would worry about it.