Hello and welcome to Just Answer.
I have seen that caused by a rear brake pad just picking up on the front edge as the wheel rotates.
Usually the fix it to remove the pads and chamfer the front edge a bit ( I usually chamfer all around the edge to a depth of about 5 mm)
Clean where the pad sits thoroughly and reassemble.
If there are any fretting marks on the pad backing buff them off with a wire wheel.
The part that needs chamfering is all around the edge of the friction lining. Do not chamfer the steel backing whatsoever.
I am working on a sketch that will upload for you.