You didn't provide much to go on, but my guess is that the beeping sound is an alert signal reminding officers that the channel in question is closed to general use and only available to officers on a specific call where there is currently a high risk operation active. It could also be something as simple as the scanner is listening to a trunking channel in conventional mode so you're hearing the system's "housekeeping" signals.
If you can provide more specifics on where and when you're hearing that "beeping noise" (e.g. "The Mayberry PD Dispatch Channel" or "Talkgroup 93275 on the Podunk ID Trunking Radio System") folks around here can probably give you a pretty good answer to what's going on.
The "garbled sound" may be one or more of the agency's encrypted transmissions. This may be confirmed if you can provide details on which channels those are as well. Assuming that you're listening to this system (
http://www.radioreference.com/apps/db/?sid=257), those with a Mode of "E" are the encrypted channels.
