1989 Subaru with a grinding sound but not in 4WD

#1

I recently purchased a 1989 Subaru GL and noticed a grinding that seems to be on one side of the hub, wheel, or axle (i.e. grind, pause, grind, pause, grind, pause, grind). It speeds up and slows down depending on the speed of the vehicle . It appears to be coming from the rear of the vehicle and goes away if I put it in 4wd or 4wdL. Any suggestions?

#2

I’m not really all that familiar with the old subaru part-time 4wd systems, but it kinda sounds like a locking hub that’s sticking. Assuming this thing actually has locking hubs.