Grinding/Buzzing noise when letting of the gas on the highway in 2wd

[greenbastard98]

I recently bought a 1998 ranger 4.0 4x4 5 speed that use to be my buddies back in highschool with a rebuilt engine but has been passed down the line atleast 3 times until it got to me so its hard to say what has and hasnt been done correctly to it. I recently noticed a grinding or buzzing noise on the highway when i let off the gas and when i get back on the gas and seems to have gotten progressively worse, most noticeable in 5th, that sounds similar to driving over the rumble strips on the shoulder or severe radio static.To me it sounded like it was coming from the passenger front hub so i proceeded to change the front wheel bearing hubs, cv axles and swapped the PVH to rugged ridge manual locking hubs thinking the new wheal bearings would fix the problem. My new parts did not fix it, i then checked all my powertrain fluids, front/rear diffs looked good, transmission looked good, engine looked good, Tcase looked terrible and grey in color so i replaced the Tcase fluid with royal purple ATF and used lucas oil additive for 1/2 quart of the capacity. changing the tcase fluid may have quieted the sound alittle at first but it is now still as loud and severe as before. i am thinking of removing my front drive line and driving per usual to see if the noise continues or changes at all. I am also not able to engage 4hi or 4lo and the lights flash intermittently 3-6 times randomly but flash especially often when i have to let off the gas with alot of momentum and the noise is especially bad. I do not here the tcase module make any noise when i try to shift into 4x4 and no lights appear on the dash in that case. Can anybody help me, share experience or point me in the right direction, this problem is driving me up the wall and after it is fixed i can go back to fixing the small nitty gritty issues with the truck like exhaust leaks, vinyl floor, shifter knob, tune ups and all that good stuff