Mine wore weird on the inside and was vibrating bad. It eventually developed a huge bubble on the inner wall. I'm guessing a belt broke. Maybe yours is having the same issue. Or the inner bearing is going bad on the hub.
Can only be 3 things
As Rfoster said.Wheel bearings
Leaf spring bushes or shackles
Bent axle(very unlikely)
Check bearings 1st as this is the most likely cause.
Hope this helps