complex to guess it accuratly by us,, interesting to be solved by u,,i would say,,, these problems realy want some time from you to check and isolate them,,
it could be the wrong/non centered placement of the hollow iron small rod type of nut on the axle...
it could be the improper chain free play adjustment,corrrect it on both sides and take ur time to make it correct on both sides..
brake shoe may be placed in wrong direction ?
if its small just leave it,, it wont matter seriously,,
however a good mechanic can solve it,,they are very picky in identifying and solving ,, onc a mechanic agrees its a problem e will solve it,,
if a mechanic says its no issue then he will never be able to solve it,,just skip to other,