Not your typical train sound, but different sources of sound overlapping can easily distract an observer into guessing or drawing a wild conclusion. Trains aren't the only machines occupying the yard.
On the topic of strange untraceable noises, yesterday standing on the front sidewalk I heard what sounded
exactly like a British WWII siren quickly winding up to about a minute of peak pitch followed by maybe ten seconds of silence only to repeat the former cycle. I have a feeling the noise carried over to my neighborhood from some construction equipment about three blocks away; it was subtle, but hearing the subtle aura of what may as well have been a Carter was eerie to say the least.
