You can't yet purchase a "ready-made" RDC sound. Like Wolfgang, I use Loksound, where you can download different sounds into the decoder with a programmer. The decoder I have in my Proto 1000 RDC SP10 is an old Loksound 2, with a modified German hydraulic sound that's "near enough".
Brian Moore
Plymouth, UK
Here's mine, Athearn and ESU Loksound. Look and listen.
Wolfgang
Pueblo & Salt Lake RR
Come to us http://www.westportterminal.de my videos my blog
There may not be such a decoder sound recording available from anyone.
Here's a link to the available sound schemes offered by SoundTraxx Tsunami diesel decoders, and there's no listing for any type of rail car.
http://www.soundtraxx.com/choose/index.php?p=choose3.php
What is the best sound decoder for a budd rail car ?.H.O.scale.