before I install this transfer-case...

[gringeltaube]

....................... I think this probably has something to do with it. I'm fairly certain that I put everything back together the same way it came apart, but I guess it's possible that I messed something up. I don't know.

Unless I missed something you never told us how you corrected what is shown in your post #4....?

It does take that spacer/ (thrust)washer (#27 in my post#6) to keep everything in correct position! Otherwise the companion flange deflector shield could now be interfering with the housing, the seal riding on the shoulder where the deflector is seated or other issues...

BTW, both style TCs have exactly the same washer behind the front output flange. Its dimensions are: 63.5x42.0x5.8mm.
Have one made if you lost both of yours!

To try to locate the problem: does it make that noise standing still with TC in Neutral? ... moving in 6x4 with front prop.shaft disconnected from front diff.?

G.