Carriages that have a Speaker in them that Play Train Sounds in time with Revolutions of the Wheels, Like Digital Sound Loco's in G-Scale
MRC makes a sound system that might be what you're looking for: http://www.modelrectifier.com/products/trainSound/soundSystems.asp Or, SoundTraxx makes digital sound/DCC Decoders: http://www.soundtraxx.com/ Hope that helps a bit. Mike C Phoenix
Aztec used to sell sound equipped cars that used batteries Deb has a mech reefer that sounds like one and another car (can't remember what sound).