Looking at the Allied Radio Matrix for Emergency Response (ARMER) Trunking System
, it looks like you have a bunch of simulcasted sites. It's possible that you are running to simulcast digital distortion
depending on what sites you are monitoring. There are some recommendations on how to improve that on the link I provided above. In any case, many scanners will probably run into the same problem that you are currently encountering.
If you are not monitoring a simulcasted site, you probably want to consider upgrading the antenna before dropping money on a new scanner. It looks like most of the ARMER system is on the 800 MHz band, so you can always try out a GRE/RadioShack 800 MHz antenna, though you should research and consider other solutions as there are many good antennas out there.