I looked at that, and it was already set to "enable".
This seemed to start about the time P301 rolled out (mid-June or so).
I just got off the phone with Dish Network. The first guy hung up on me while "transferring" me to someone else. The second gal seemed nice but ultimately had to ask her supervisor about it, who apparently told her that the constant running of the disk is "normal".
I have had this box since 2002, and I do not remeber the disk ever running all the time.