The squeal I posted on 11/11 at 11AM might be less grating than the horseshoe curve audio below - but any MP3 can be used. Just store it as 001.mp3 on track 01 and wire your trigger/sensor to terminal 01 (or send a DCC play command or function command). When terminal 01 is triggered, it plays. You could also put another trigger at the other end of your curve to make it stop.