There is the Soundtraxx SoundCar decoder, but it doesn’t take the place of the loco’s decoder, just adds other sound effects further down in the train.
I agree with the other posts, upgrade to a LokSound and enjoy the excellent sound files and motor control. I did a Bachmann 2-10-2 a couple years ago, and have a K4 in the queue (I may even do it this week, if my allergies subside).