Perhaps if you are living in a frigid climate, especially during the evening hours the map disc, including discs in your CD changer will have a thin film of condensation on them. Once the temperature of the rear trunk area rises, the condensation should dry and you should not experience this. If your rear seas fold down, then make sure the rear vent is open and blows warm air into the trunk area with rear seat folded down to expose the trunk, if problem goes away sooner than before this is it. By the way v28 is available in the navigation area of this site which is most recent operating system release.

Good Luck.