Could also be leakage from a cable tv system. CATV channel 18 around there. 73s Don

Before you get software, remember that DRM requires a signal from the IF before detection and a bandwidth of about 15khz(I'm not sure of the exact value.). This means modifying the receiver or getting one with an IF tap. If what you are hearing is 850 shift, then you are hearing some type of data mode (Rtty, or newer system). Try the following links,
DRM http://www.drm.org/

Audio of various data modes http://www.signals.taunus.de/

73s Don NJ2E