While monitoring the James City/Williamsburg/York County system with Pro96Com, I observed York County units displaying a "Type Field" as "PvtData" and "GrpData". During these displays, I did not hear any audio on the system nor was a talkgroup displayed. When I looked at the Channel Grant Trace Screen it showed entries for "GrpData" in talkgroup "-1". The "PvtData" was not displayed on Channel Grant Trace. The anomalies only occurred on three York County Police units. While this was occurring, you could read the radio ID numbers. The same radio would transmit at different times unencrypted and with normal displays. It appeared that only these three radios were generating the strange "Type Fields". Could it be that these radios were synchronizing with the system? What's the difference between PvtData and GrpData? Why is it only happening with the York County Police units?