Digitrax definitely did make one and it was programmable so you could load what you want onto it. You might find a few of them still around.
Richard
I think QSI makes one, check there.
Check the web sites of the companies that make sound only decoders and see if they have such a thing available. Digitrax ? SoundTraxx ? MRC ? ESU LokSound ? It all depends on whether they have a sound only decoder with the proper sounds that you're looking for.
http://www.digitrax.com
http://www.soundtraxx.com
http://www.modelrectifier.com
http://www.esu.eu/en/start/
I have installed a non-sound decoder in my Bachmann Gas Electric and would like to add a sound only decoder which would produce motor sound at least something like the prototype. Any suggestions for this application?