Here's the pictures. There are two Union Pacific engines. The one with the screw behind the stack is the one with the Diesel Roar. The other Union Pacific has a hole in it but no Diesel Roar. Then the Santa Fe that doesn't have a hole at all.
Funny thing is, I just got it in the mail today and put it on the track to try it out. Well it made this terrible noise like something was rubbing one of the gears so I go tearing it down to see what's going on. That's when I notice there are two wires that are still attached to the shell. So I jump the thing to get it to run and I can't see where anything is rubbing. But I still hear the noise. So I start looking closer and the noise is coming from the shell. The part that you see in the middle of the picture with the cross on it just vibrates back and forth making the noise. It probably is hollow and has something rattling around inside of it.
So there we are. I learned something today.
Thanks for all the help and references!