John,
Sorry for the delay, but the NM Railrunner does have the "beep beep" sound.
My sister was out in NM and heard it on the doors. If you find some videos on Youtube with someone riding in the cab control car you can hear the alert. I have road other commuter trains and they all have different alerts or none at all.
I found this company that has some pretty cool stuff for lighting your cars, etc. They sell HO and N stuff. www.sbs4dcc.com
Anyway if these electrical pickups work I will probably add lighting and sound for the control car using a TL-1/4 decoder. If I can download the "beep beep" sound for the doors I might give this a try. The only thing is that I would have to do it for all of the cars.
The other option would be to place a sound system in the station stop or under the track at that location. I then could use an on/off switch for a couple of seconds. The volume would be high enough to hear it only at the station stop. I might even consider an announcement saying "door closing" and then the beep beep warning.
Just a thought. If the car lights and sound install works I will let you know.
Len