Frankfast, One of my CR18 rims had a piece of flashing come loose when they were new. The rattling was just too much to take and while it took more time than I wished, the little bit fell out. I also lucked out once removing a piece of welding rod from the RHS chainstay through the rear derailleur cable stop's screw hole. That happened on my first try and I was amazed as it usually takes longer to remove a pick from a flat top hollow body!

I didn't have to with the rim, but plan two was a shop vac.

Brad