I recently replaced my bad rear diff with a non howling one, all is... (was) good until I noticed a grinding/vibrating/humming sound from underneath. Turns out the rear companion flange nut was extremely loose. I un-staked it, removed the nut cleaned 'er up a little bit and reassembled. Torqued to the 90 ft. lb. specs and the problem significantly lessened. Previously I would be going down the road and could feather the gas and it would make the horrid noise, which would last for a long time. Now it'll happen after I'm done accelerating and let off the gas for about a second. Granted it's not horrible, but still annoying I'd like to eliminate the problem completely.

Is it not tight enough? Or could the transfer case rubber mount be worn out? I do see a large square rubber block below the t-case which is not actually touching the bottom, not sure if it's shrunk or what's going on with it.