If you're sure that this is the issue, putting physical space between the On Demand system and the scanner may be a simple solution.
Unplug the antenna on the 15X and see if the interference goes away - if so, something in that system is radiating, and needs to be isolated. Shorten up every cable you can - even wrapping them in a coil, and tied off with wire ties, has been known to help. Long unshielded cables can act like antennas for RFI
I would try to isolate the power supplies - it's not unheard of that RFI gets transmitted from an unshielded power cord (and these power cubes that come with scanners have next to no shielding). If you can run your 15X on a separate power plug, do it. Wrapping the cord around a ferrite core (or putting beads on it) may also help, if the power supply is indeed picking up the radiation.
Indoor antennas are an unfortunate necessity for folks living in condos and apartments. But if you have access to an attic, put something up there with very well shielded coax, and the chances that the coax picks up the RFI greatly diminsh. Putting the antenna as far away from the source is also a very good idea.
RFI issues like this are tricky - they're not easy to solve, if they can be solved at all.
GL.....Mike
