The rattle is the OIS stabilizer- as mentioned on nearly every DVX100 FAQ on the Web. It is normal and you will not hear it when the camera is turned on.
Just about any camera will react to fast pans over high contrast areas.
The headphone jack can be an issue depending on your setup but will not affect recording quality.
As problem cameras go the DVX is pretty much at the bottom of the list. But then again you did ask on the DVX100 forum so…
Noah