To KHP...If the agency your refering to is using "securenet" for encryption,then entering the 152dpl should mute the noise. I'm suggesting this because of a local pd that uses the same encryption standard,and it's tone of 146.2pl is not transmitted when code is on.
Now if it's single inversion scrambling as mentioned,then maybe a DNE (don noble electronics) decoder would work nicely if installed in to a external speaker.
I've had a DNE for years,I use it to decode some of the bubble pak radios that have the scramble feature.
N9ZAS.