"Motor" sounds on B. radio??

[EJA]

Beethoven radio just played Appalachian Spring, and I could swear I heard the faint sound of cars driving in the background. It sounded as though they were shifting gears after being stopped at a light. I've heard this before, but am not sure if it was in Appalachian Spring. Has anyone else heard this? Is it something on the recording or is it cars on Assylum Avenue? Is it part of the music? Is it my imagination?