Rattling noise from Lionel PS-2CD Covered Hopper cars

I purchased two sets of the new Lionel PS-2CD Covered Hopper cars (Lionel Nos. 2442110 and 2442130). The cars look awesome but about half of the cars make a rattling noise like something has come loose inside. Does anyone know what might be causing that? Is there an easy way to take the car apart without damaging anything?