Grinding noise/Vibration when rear wheels slip

[jmatteis]

So, about a year and a half ago, our 2006 Explorer XLT 4.0litre, starting, very rarely grinding, or vibrating around 70 km/h. It was awful and felt like the engine was working harder to keep speed. but it would go away. This winter, anytime the rear wheels slip, the grinding comes, around 40 km/h. When the vibration wouldn't go away, I could hit the 4x4 high and then auto again and it would go away. Last week, just had front diff rebuilt, and it seems to be better... The vibration is not as bad, even if I put it in 4x4 high. However, my wife drives this mostly and she said that it's still doing the same thing, the vibration is not as bad, but if the tire slips, the grinding is there, and will only stop if she hits 4x4 high then auto. So, it's like the transfer case engages but won't disengage... I'm taking it back to the transmission guy this week, he showed me the bearings and rings pulled out when he rebuilt, and they were scored pretty good... I imagine that if the transfer case has been engaging and we've been driving in 4x4 not realizing it, that would have caused excessive damage...

any thoughts on what causes the transfer case to not engage... or if I am way off thinking it's transfer case??? Any suggestions would be appreciated, to try and trouble shoot this with the mechanic... I love the truck and would rather fix it than have to buy another vehicle...

Lastly, my wife was rearended OCT 2013, and the vehicle that rear ended her was totalled, the truck was pushed forward a foot or so, rear door pushed in. Could an impact like that cause problems with transmissions or transfer cases not lining up, etc.. we had no problem like this prior to the accident (could be coincidence, I know)

Thanks