I have a 2007 Sierra 2500HD (new body style) with a manual transfer case. With the transfer case in 2wd the 4x4 indicator on the instrument cluster will come on occasionally (4x4 does not engage). It seems to be random length of time that it stays on for, but if I shift the truck in and out of 4x4 the light switches off. Does anyone have any ideas as to what might be the cause of my problems