I have a 2002 Kia Sprtage 4WD SUV. Whenever I get going it tries to engage the front whel drive shaft amd starts to make a humming noise. When I go to stop it opos back out of driver into 2 WD. The 4WD works great when I engage it but not sure why the transmission seems to want to engage it itself. I thought it might be the transmission or T-case. Any ideas? Thanks.