The rebuild option on the Karma is in Menu -> Settings -> Troubleshooting -> Rescan Music. This can take a while, depending on how full it is. I could've sworn there was a "Restore factory defaults" option, but can't find it now.

I'm not sure what to tell you about the heat when docked. I do remember mine getting hot like that from time to time but tended not to keep it docked for very long after the battery was fully charged.

I would just be on the lookout for any ominous bulging.

Good luck.

ps. Keep an eye out for the 32 GB flash version of the vibez due out in the next month or so. Just in case.

pps. Now that I pulled my Karma out for the first time in months, I had to plug in my SR-60s and give it a listen. I love my vibez, but damn the Karma sounds good.