Originally Posted by CSP
Sounds like you need to drail the oil on one gearbox at a time and check for metallic residue in the oil. I'd start with the transmission. You can also remove the shifter tower and look inside to see if anything glaring sticks out. A '73 wouldn't have ever had a catalytic convertor.
Drained the transmission and transfer case oil. Didn't notice anything significant with the oil, no metal shavings other than obvious wear from forty years of use. Refilled it with 75-W90 and some Lucas. Took it for a ride and the noise is still there. Thinking very seriously about a fuel injected 4.0 and AX15 conversion