Fire is not generally encrypted, so if you are not hearing any fire traffic it is probably not encryption. Madison county used to be multicast over the sites located in Bonneville county, but that stopped a while back. Multicasting of Fremont and Clark counties has also stopped. Are you able to hear any Clark or Fremont county traffic? They use some of the same transmitter sites as Madison.
Depending on where your located and which transmitter site you were picking up, it could be changes to the control frequencies., although I am not aware of any changes made to the FCC database as far as frequencies go.
I'll have to look into this and see if I can find out what has happened.
Dave