noisy hubcaps

I recently bought a nice 2003 Mercury GM but a couple of center caps were missing. I bought a set of four on eBay and discovered that there are probably a dozen look-alike center caps that only fit certain models and wheels. My car has 16 inch flat steel rims with bolt-on hubcaps -- normal hubcaps won't fit. I have tried adjusting the pressure on the plastic bolts according to instructions but the hubcaps rattle on every bump in the road. A new center cap costs $59 and used ones on eBay run about $30-40. A nice gift from Mercury to cap thieves. The center caps can be quickly removed, placed in a coat pocket and sold on Craigslist or eBay for enough money to buy drugs. I have been told that only the 2003 has the noise problem. A new set of hubcaps with center caps costs over $600 and they will probably rattle. Have any owners discovered a cheaper solution?
Ralph