Originally Posted by Mike
Pull the battery from the FOB to eliminate the FOB as a suspect first.
Excellent idea. I've found that when the battery begins to die in fobs for Chrysler vehicles, the fob will send a signal to the vehicle to lower the windows and unlock the doors. Newer Nissans will pop the trunk and unlock the doors. Newer Hyundai'* will pop the trunk and beep the horn.
Maybe GM has incorporated some type of feature into thier system as well.