The last snowstorm we had here in NJ my wife drove the Trailblazer around in 4WD/AWD and when she disengaged the next day after the roads were cleared it sounded as though the front rear wasn't releasing all the way and had a faint winding sound to it. She made an appointment with our local service shop (her cousin) last friday, but in the meantime the truck stopped making the noise which would seem that it finally worked it's way fully out of 4WD. On her way over to drop the truck off a few days later, we got more snow, she turned the selector to 4WD and BAM!! She said it sounded like she was dragging something under the truck. Wayne put the truck up on the rack and found the casing was cracked. So we are off looking for a salvage yard part. The only thing I can think of that would cause this kind of damage is possibly water in the front diff that froze. Any other thoughts out there??? Also.....I think she went from 2WD to 4WD HI while on the go, but I don't remember in the manual if that is a no no or not.