Recently, I took my 540040 and turned it into a 717 hour unit by adding a pair of 320GB hard drives. Unfortunately, one of them is obviously starting to fail. I can hear the clicking the sound on occasion in addition to the occasional freezing of the picture. I have a couple of questions: 1) What is the easiest way to determine which drive is failing? 2) Is there a process by which I can replace one of two married drives with another hard drive of the same size? 3) Am I going to lose all of my stored data? We've got a ton of TiVos, so I can easily transfer files if need be. I just need to know whether the process is requisite before getting started. Any help you may offer would be appreciated.