1989 XJ, D30 front D35C rear. 4.0, AW4, and NP231 from a '92 (according to the PO).

This noise first appeared first of August. It goes something like -lunk- -lunk- -lunk -- at the time it was only on deceleration with left turns, yes, only on left turns decelerating. It always appears to be emanating from the rear of the vehicle. Also at the time, I thought it was a wheel bearing starting to go because it would only sound on left turns and sounded as though it was coming from that wheel. I replaced both rear wheel bearings; first the left then the right a week later. The noise did not change.
Life got busy and I decided to let the issue get worse so I could track it down better -- maybe.
The Last of Sept I needed to take a 350mi round-trip road trip for my job. As I traveled the noise got worse and worse. Back home now, the noise is really bad and happens not only on left turn w/decel but also sometimes while traveling at constant speed and straight driving. It never sounds on right turns! Oh, did I say, it never sounds on right turns?

I jacked the truck up and ran it in drive, wheels off the ground and using a stethoscope listened to everything I could see. Only noise I found was a faint -tick- -tick- -tick- coming from the rear output shaft of the NP231.

Further testing while driving: applying hand brake while decelerating makes the sound appear to come directly from beneath my seat or beneath the hand brake.

Am I looking at a Tcase swap or is this a symptom of needing a new chain? Any ideas will be welcome. Thank you in advance...