Another group to consider: http://groups.yahoo.com/group/socalscan
Why don't you join that group and ask them?
In addition to hearing the annoying buzzing noise, your scanner may display a combination of Letters and Numbers below the frequency. If it does, that is the System ID which identifies whose network you are picking up.Here's how I know.
You tune in to the frequency and I hear garbage noise that hurts my ears. That's the control frequency. When one hears it, it becomes obvious it's a trunking system.