98 Explorer XLT 4.0. I have tried researching this, but there isn't a clear answer. My dash has 3 options: 2wd, 4wd AUTO, and 4 low. From auto to 4low it grinds and I can hear it switch. From auto to 2wd, there is no noise at all. No switch. Lights show up on the dash like they're switching, but...