Have you tried doing a non-volitile memory dump?
It won't wipe the drive or your settings, but it clears corrupted entries in the EPG - it also does a complete reload of the system software. I tried it and it did WONDERS for my unit - no more guide errors, no more time delays, so far no GODeath or VODeath (knock wood)... seemed to stabilize the unit (for now).
Here's a link to the post that mentioned it:
http://www.satelliteguys.us/showpost.php?p=222596&postcount=10
(it's info for a 710, but I tried it and it worked on my 522)
But if the system is REQUESTING a disk rebuild, the HD may really need it bad... not sure if that trick will work for you.