What could be grinding in rear somewhere from the transmission to the rear end when moving down the street

see if this link helps you..
Four Common Car Noises
or this one.
https://www.google.co.uk/webhp?sourceid=chrome-instant&rlz=1C1CHBD_en-GBGB719GB719&ion=1&espv=2&ie=UTF-8#q=real+loud+whining+sound+in+my+front+end+while+driving+down+the+street

If the car is still moving forward when you are placing it in gear, there are a few things to check.
look under the vehicle and place the car in stadard 2wd, and try to move the car forward. watch the rear end to see if it buckles, and watch the driveline to see if it is spinning freely or catching up. Check the U-joint for the rear end. See if the SUV is able to be pushed backwards and forwards.
The fact that it will not move in 2wd, but it moves in 4wd, makes me think that you are not having a xfer or transmission issue, but one in the rear end. Spider gears could have failed, or it could be something as simple as a U-joint.
Feel free to send me pics, and let me know how that goes.

It sounds like you have a bad axle

My guess would be the transmission because of it rolling in park.

sounds like rear end is coming apart
google wrangler forums and post there

Check and make sure the bell housing on the transmission isn't broke and trying to separate from the engine. Shifter shouldn't move while cranking unless transmission itself is moving.

definately sounds like a bad strut to me

Sounds like something is caught up inside or outside the engine/transmission where a part is grinding from something reciprocating. Does the sound happen when you apply the gas without the car moving? If the sound only happens while moving then it could be suspension or transmission related. If it only happens with or without the car moving as long as you control the gas then it's probably in the engine or transmission related. Could also be a wheel bearing issue, that will be a humming sound inside the cabin. As you speed up the pitch increases and the opposite happens when you slow down.

I would investigate the transfer case. By your description here it sounds as if the gears inside are worn and the drive chain inside is rubbing, causing the loud noise you hear.

check the rear dif.