Noise from t case or auto trans.

[Geren8509]

So, I have a 1998 qx4 with 190,000 miles on it. It snowed here today and I used the "auto" setting for my 4 wheel drive, I pulled into the garage and noticed when i put it in reverse or drive, while in auto or lock 4wd, there is kind of a howling/whining noise, maybe a grind? It almost sounds like a dry bearing spinning or something. But when i take it out of 4wd it goes away and only does it when im in drive, 1 or 2 and reverse while in auto or lock. Can anyone help me here? I replaced the t case fluid about 1,000 miles ago and it was just dark, no noticeable metal shavings. And i pulled the transmission pan and replaced the filter about 3,000 miles ago. It had the usual metal shavings on the magnet but not excessive. I wouldnt expect my problem to be in the transmission because the noise only happens when i put it in auto or lock 4wd while in gear, but the noise goes away while i am in neutral or park in auto amd lock. but im not sure. Can anyone help? I seen other threads on issues with 4wd while driving or something but i havent noticed any driving issues. Auto and 4wd lock both work fine. Any help would be appreciated much!