you will need to check it out, but it could be that the diff has shifted on the springs. due to sheared off pin or mount etc


get under it and check if the chassis has any creases or wrinkles, cracked out paint. it would be a hard hit to bend the chassis (tho they are not particularly beefy, but if what you say is true then im betting its hit the wheel)

a 4 wheel alignment isnt going to help becasue there is no adjustment in a leafspring rear. you will need to check the leaf springs, hangers, U bolts, diff mounts etc for damage.
The sound is the tyre scrubbing because its not pointing in the same direction as the rest of them.

If the chassis is bent, its pretty affordable to get them on a chassis machine and straightened out, these are real basic trucks



so. in summary
inspect the chassis of the truck for signs of deformation
inspect the rear suspension for signs of damage

I believe there are some shassis and suspension measurement points listed in the manual. all you need is some chalk, a plumb bob, a tape measure, and some flat concrete to park on