I've noticed this twice in my 2006 model and I haven't had any moisture problems. I "cured" it by applying the emergency brake briefly and it went away. I'm wondering if perhaps the calipers might be sticking slightly. I intend to bring this up when I take it in for my first oil change an filter. It really shouldn't be doing this, although I don't believe it is a serious matter. Disks are different from drum brakes in that the pads are always in slight contact with the disks unlike drum brakes which retract and there is no contact. If it were serious enough, it could warp the disks. Shouldn't be assumed to be normal.