Grinding in reverse
 

My 1996 Suburban started this yesterday. Right now, if you put the transmission in reverse, there is a very loud grinding noise, and the speedometer goes up to about 15 even though the vehicle is STOPPED. It doesn't grind in drive, and thought it could be the transfer case although it does it in 2H, 4H, and 4L.

It has a NP241 (electrically controlled)
4wd hadn't been used in 2 months
4L60E (I've heard the sunshell fracture causes similar symptoms)
the fluid in the transmission is 1 year old, is bright red, not burnt. Filter was replaced at same time.
All u-joints look good.
Also, when I towed it home (about 1/2 mile) I kept hearing a clunking noise.
No holes or anything in the trans or transfer case.
No check engine light.

I haven't verified fluid level/condition in the transfer case.

Has anyone had these symptoms before?