I picked up one of the new PS-1 sound boxcars, in my case the UP 'flat spot' sound car. Decent looking car with nice detailing and paint. I flipped it over and a couple of interesting discoveries. First of all, it was made in Vietnam, I wonder if China is getting worried? 
Next, no labels on the switches! So I look at the tiny piece of paper that I overlooked the first time, and it identifies the switches as MIN/MAX and SOUND/NO SOUND, seems pretty typical.
HOLD THE PHONE! They don't actually work that way! There is no switch setting that produces no sound! There is actually three different sound settings, one with the flat spot and a whole lot more background sounds. One with lots of background sounds and normal rolling sounds, and then when you switch to min, you get flange squeal and a little background sounds, the other switch doesn't affect that track. In order to accomplish no-sound, you will have to turn the volume down. Of course, I'm happy with that, I like the idea that you have three different sound features instead of just two. 
