Rear Door Locks Won't Lock/Unlock??

Just bought a new body style 2007 2500HD LTZ Crew Cab and noticed the rear door locks will not lock/unlock with the driver/passenger controls or with the keyless entry. I have to lock/unlock them by hand. It is obviously still under warranty and I can take it in but I wanted to see if there may be something I could try first. I checked all the fuses, the safety locks on the doors and the Driver Information Center options. These were all OK. Any suggestions before I take it in? Thanks.

Could it be a relay? Any idea where the relay would be and how to check it?

Check to make sure that child locks aren't enabled. Anything else you do may void the warranty, so take it in.