Originally Posted by
keithdunlop
What I've learned after some research is that this is a common issue with Open Pro rims. Apparently, there is a little piece used to align the rims when welded that is held in place with couple of dimples punched into the rim bed (see image). This little piece breaks loose and rattles around between the islets. People fix this by either punching deeper notches in the rim or drilling a small hole and injecting glue or epoxy.
I wouldn't expect the joining sleeve to come loose - it should be a snug fit in the rim cavity before they punch it, and thoroughly wedged in place afterwards. That is after all the only thing aligning some rim models that aren't welded at the join. But as you wrote, if that is the problem then drilling a small hole and injecting Gorilla glue or similar should stop it rattling.