WILLIAMS RIO GRANDE LOCOMOTIVE #5720 sound activates about 10 seconds on its own & then stays on making a loud/ugly sound.  Only turns off when I hit the Bell on the transformer.  If I hit the Bell button every 7 or so seconds the Ugly sound does not come on.  No switch for turning off sound.  Can you remove the sound card or is there something inside the unit that you can adjust to turn off the sound ??