According to Lionel Customer Service Lionel AF RailSounds boxcars (four were produced) must be used with a power source that generates chopped sine wave AC in order for the bell and whistle or horn to be activated. If you use a postwar transformer like a 30B which generates unaltered sinusoidal wave AC and one or two 6-5906 Sound Activation Buttons per the Owner's Manual for example the bell and whistle/horn will not activate while the boxcar is in motion and only intermittently at best while the car is at rest -- 9V battery in it or not, regardless of the direction it is facing, and with 6VAC or more to the tracks per the owner's manual. So if you use them with a modern transformer and buttons, or PowerMaster, TPC300 or 400 with a Cab remote then AF RS boxcars are a lot of fun especially behind your conventionally controlled postwar AF engines without those sounds. But with a postwar transformer they are not such a great experience. One thing to keep in mind -- chopped sine wave AC will burn out the speakers of your postwar AF engine diesel horn or air chime whistle sound systems so don't use them with a power source that works well with your L/AF AF RailSounds boxcars. One other thing, some L/AF equipment released more recently than the RailSounds boxcars such as 6-4402X FlyerChief/Bluetooth Berkshire steam engines in transformer mode will work fine (bell and whistle trigger) with a postwar transformer (e.g. 30B) and one or two 6-5906 buttons because their electronics have been evolved to work with chopped AC and unaltered or pure AC. Of course, your classic AM 4-6-2 Pacific, for example, bell and whistle will work fine with unaltered AC and buttons because they were manufactured prior to chopped, but also work with chopped as well.
PS I discovered this firsthand after converting from TPC400 with Cab1 conventional control (the RS bc sounds worked fine) back to a 30B with 6-5906 buttons (my two RS boxcars' bell, horn and whistle then failed). So I called Lionel Customer Service and got the scoop thanks to Kristen.
Livin' and learnin'
Sometimes the hard way.