I would suspect the big rattles are from the u joints being shot (really loose). this will cause a big racket in 4wd on the street even without the hubs locked. That would be a different issue than why your tcase accidently went into 4high. I would look into that issue first.
See you on the trail
Couple o' FJ40's, BJ70, PZJ77, UZJ100, TDI