JA,
That is unusual. I 4 wheel and I've never had my brakes squeal. On the other hand, my friends Tahoe starts squealing as soon as it hits a dirt road. I'd definitely get it checked out as it is not normal. I've rinsed my rotors off, but first thing in the morning after the truck sat all night. I didn't want to take the chance of cold water on a hot or warm rotor.