Car Analogy

I'm also betting on both sounds from same issue, as well as issue being brake related.

Someone mentioned shoes. Our cars don't use shoes for e brake (inside of rotor used as drum). Instead, rear caliper is also cable operated e brake.

Pads sometimes develop a ramp shape as they wear. Thicker on one end than the other. That could explain why noise is different in reverse. Instead of rotor brushing against pad pushing it away, shape makes it tend to pull it in.

So in addition to other good suggestions, check for cracked rotor, heat shield rubbing, pad clips incorrectly installed, examine padsfor uneven wear.

Also check glide pins to make sure caliper can slide properly.

Oh, one last thing, make sure e brake isn't dragging. Make sure rear wheels can be spun easily by hand when jacked off the ground. Compare to how easy to spin fronts for reference.