This morning my 4wd worked fine. We got 6in. of snow last night so I needed it. I forgot to switch out of 4wd when I parked at work. After work I backed out of my spot. The drive line bound up a bit, reminding me that it was still in 4wd. I switched it back to 2wd and drove home. When I turned onto my road I needed 4wd again. I switched to 4wd high, the indicator light lit up on the dash but didn't engage. When giving the engine some throttle I could hear a mild grinding noise from the front end (when rear wheel would spin). When I arrived home I shifted into 4wd low and moved back and forth in my driveway. The truck's 4wd still wouldn't engage. I could still hear the grinding though. Any suggestions?