Your profile says you're in Washington (state), but not where, as that could be anywhere from the Vancouver/Portland area to Spokane to the Walla Walla metro area, because I can't just assume the Seattle/Tacoma/Olympia metro area. Add to this, that your SDS100 may not necessarily be in the same place as your SDS200, so it might not be the IF causing interference directly. (Some devices transmit low-level RFI, and you might be close to one, causing intermodulation with the IF.)
Sorry for the nitpicking, but there are so many factors to consider, to weed out what's actually causing this interference. This is also why it would be nice to know which CC frequency on what system, especially to see if broadcast FM is a cause for interference.