number13va

Hello I have a 15 Gmc Sierra 1500.. I am getting a service 4wd message at start up and randomly while driving. Just before I get this message while driving I can hear what sounds like the front diff trying to lock in. Slight roaring noise for about 4 seconds from the front end then goes away. I suspect the actuator motor is bad on the diff. Does any one have any info on this.. Thanks