Transfer case noise when in Reverse with brake on

[fixkick]

Gearbox in Reverse Foot Brake Held.  NO advance of the throttle.  Rattling heard in transfer case.  My head was right next to it and it wasn't the drivelines.  I will search loose transfer case chain.

diagnosing noise on any machine is not easy, and even can be very dangerous. 
but in your case the car is 0 miles MPH, zero speed so is 10x more safe this noise.  finding it 10x more safe. but you are in gear, and car can move if you are under it, then.
A/T in REVerse (this is called the A/T stall tests. classical and does overheat the clutch, so do for 5 seconds, stop rest it for 1min repeat so no damage to clutch , ok?)

foot brake set, hard, in 2wd (less parts  spin in 2wd so testing this way is best if it fails and does)  a mechanics stethoscope $5 tool is handy here, to hear WHO is making noise?

For sure the cheap causes, are U-joints.  have them inspected if you have never done them (replace or tested) them and have them checked out .

The chain fails mostly if you let other drive the car in 4wd (means front locking hubs are locked ) on dry road, rain wet only roads, or any road not slick with ice, or snow or on mud or dirt, this car has PART TIME 4 wheel DRive, and when it true 4wd one tire, most be on a slippery surface or the chain will bet damage, (streatchging and is progressive damage)
in 2wd the chain just floats.

see part ID 29 here
https://fixkick.com/tranny/xfr-case/html/image_1.html
that device there the DOG gear, is unlocked in 2wd, so the chain and all parts below it at ID33 etc,  float (means free wheeling)

it rattles at idle, keep and open mind on what can fail, even transmission mounts bad, or just loose.
check all related bolts there yet? on mount and rear trans cross mount every part if it for damage or loose parts.? or offroad damage?>

any good suspension shop can find noise, they do it on a lift, far more safer, 2 men testing for noise,  the test is easy, not moving , in REV, at idle.
and the 2nd guy finds the noise, by sound, by looking for parts moving oddly there, (under car) and levers all parts, key off, then levers the mounts off and running, to find if something is just simply loss, or the classic bad JOINTs.
if you car is 25 years old and the U-joints are day 1 factory parts that old why think they are good.  that grease it them turned to dust long ago.
you can buy forged joints (not cheap ones) with zerk fittings and grease them every 1 or 2 years and can last longer.
but most JOINTS make big fuss moving fast and under changing loads, and shifting and all wild throttle actions, moving.
parked noise, only is very odd, but can happen.
see Scotty too, below,
https://fixkick.com/NOISE.html