The caps have nothing to do with this problem. It is the ORIGINAL chip in the decoder. It was crippled thanks to a frivolous lawsuit by MIKE'S TRAIN HOUSE claiming he invented the DCC technology for sound. QSI had to "cripple" those features until the suit was settled (Mike LOST). The only cure is to purchase the upgrade chip . They are available from Litchfield Station. The upgrade will cure that problem plus open up features like BEMF. I was a BETA tester for the upgrades and programmer. I have over 15 OEM decoders with upgrade chips in them and none has had the problem return.
The chips can be purchased pre-programmed with the correct sound file or , if you know someone with a programmer, they can load the correct file for you.