Same year & model here except that mine has the automatic locking hubs.
Once it gets up around 40 mph there's a whirring noise like a bearing spinning then a "bang" with something engaging or disengaging.
Sometimes there's a nasty shake on the driver's side tire.
There was about of 75 deg of play in the steering wheel so i knew that the steering box had to be replaced. Replaced that & checked the rest of the front end. It looks reasonably good so it's less likely to be in the steering.
Point being: Even though the 4 WD is disengaged the drive shaft going from the pumpkin to the driver's side wheel seems to be turning at least some of the time.
Combine that with rusty U- joints & dry pavement and all kinds of things can happen.
At least that's the current idea of what might
be going on.