First, double check that your unit really is V4 ( see "Finding Out The Current Software Version" UM p.57). This sounds like an issue that was present in an r=earlier version.
If it is V4, I would suggest that you try the procedures described under "Fixing Strange Behavior, Freezes, Etc." on UM page 53.
If it proves to be a hardware problem and your unit is less that a year old it should be covered under warranty.
