I'd get it on a lift, and place it in drive, and listen to where grinding noise may be coming from with inspection. Front prop shaft inspect.
Re : Part time light- Transfer case position switch.
https://www.jeepkj.com/threads/how-to-change-transfer-case-position-switch-v2-0.63327/
Have you recently engaged or selected any 4x4 modes?
When u turn steering wheel on ground while driving, does it feel like it is binding in a turn?
Rear diff gear oil, spec is drop diff cover every 20- 35k miles.
I use lucas 85w-140 dino gear oil- do not use synthetics in rear diff.
Transfer case is ATF +4 , remove fill plug, ensure it is not leaking / near full.
Front diff- dino too, is it near full?